Wavelength division multiplexers for space division multiplexing (sdm-wdm devices)

ABSTRACT

Wavelength division multiplexers for space division multiplexing can include wavelength division multiplexing fanout devices or pump-signal combiners for multicore fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/416,859 (Attorney Docket No. CHIRA.045PR), entitled “WAVELENGTHDIVISION MULTIPLEXERS FOR SPACE DIVISION MULTIPLEXING (SDM-WDMDEVICES),” filed Oct. 17, 2022, of U.S. Provisional Application No.63/424,812 (Attorney Docket No. CHIRA.045PR2), entitled “WAVELENGTHDIVISION MULTIPLEXERS FOR SPACE DIVISION MULTIPLEXING (SDM-WDMDEVICES),” filed Nov. 11, 2022, and of U.S. Provisional Application No.63/488,421 (Attorney Docket No. CHIRA.045PR3), entitled “WAVELENGTHDIVISION MULTIPLEXERS FOR SPACE DIVISION MULTIPLEXING (SDM-WDMDEVICES),” filed Mar. 3, 2023. This application is also acontinuation-in-part of U.S. patent application Ser. No. 17/183,136(Attorney Docket No. CHIRA.044A), entitled “SPACE DIVISIONMULTIPLEXERS,” filed Feb. 23, 2021, which claims the benefit of priorityto U.S. Provisional Application No. 62/980,884 (Attorney Docket No.CHIRA.044PR), entitled “SPACE DIVISION MULTIPLEXERS,” filed Feb. 24,2020, and to U.S. Provisional Application No. 63/001,814 (AttorneyDocket No. CHIRA.044PR2), entitled “SPACE DIVISION MULTIPLEXERS,” filedMar. 30, 2020. The entirety of each application referenced in thisparagraph is expressly incorporated herein by reference.

BACKGROUND Field of the Invention

The present disclosure relates generally to an optical coupler array,e.g., a multichannel optical coupler array, for coupling, e.g., aplurality of optical fibers to at least one optical device. Someembodiments can relate to coupling light to and from a plurality offibers, such as to and from one or more single mode fibers, few-modefibers, multimode fibers, multicore single mode fibers, multicorefew-mode fibers, and/or multicore multimode fibers. Some embodiments canrelate to coupling light to and from photonic integrated circuits (PICs)and to and from multicore fibers (MCFs). Some embodiments can includewavelength division multiplexers for space division multiplexing(SDM-WDM devices), including wavelength division multiplexing fanoutdevices and pump-signal combiners for MCFs. Some embodiments can includespace division multiplexers (SDMs), including adapters between MCFs withdifferent core patterns and/or add-drop multiplexers for MCFs. Someembodiments can relate generally to high power single mode lasersources, and to devices for coherent combining of multiple optical fiberlasers to produce multi-kilowatt single mode laser sources. Someembodiments may relate to phase locked optical fiber components of amonolithic design that may be fabricated with a very high degree ofcontrol over precise positioning (e.g. transverse or cross-sectionalpositioning) of even large quantities of plural waveguides, and that maypotentially be configurable for increasing or optimization of thecomponents' fill factor (which can be related to the ratio of the modefield diameter of each waveguide at the “output” end thereof, to thedistance between neighboring waveguides).

Description of the Related Art

Optical waveguide devices are useful in various high technologyindustrial applications, and especially in telecommunications. In recentyears, these devices, including planar waveguides, two or threedimensional photonic crystals, multi-mode fibers, multicore single-modefibers, multicore few-mode fibers, and multicore multi-mode fibers arebeing employed increasingly in conjunction with conventional opticalfibers. In particular, optical waveguide devices based on refractiveindex contrast or numerical aperture (NA) waveguides that are differentfrom that of conventional optical fibers and multichannel devices areadvantageous and desirable in applications in which conventional opticalfibers are also utilized. However, there are significant challenges ininterfacing dissimilar NA waveguide devices and multichannel deviceswith channel spacing less than a diameter of conventional fibers, withconventional optical fibers. For example, in some cases, at least someof the following obstacles may be encountered: (1) the differencebetween the sizes of the optical waveguide device and the conventionalfiber (especially with respect to the differences in core sizes), (2)the difference between the NAs of the optical waveguide device and theconventional fiber, and (3) the channel spacing smaller than thediameter of conventional fibers. Failure to properly address theseobstacles can result in increased insertion losses and a decreasedcoupling coefficient at each interface.

For example, conventional optical fiber based optical couplers, such asshown in FIG. 6 (Prior Art) can be configured by inserting standardoptical fibers (used as input fibers) into a capillary tube comprised ofa material with a refractive index lower than the cladding of the inputfibers. However, there are a number of disadvantages to this approach.For example, a fiber cladding-capillary tube interface becomes a lightguiding interface of a lower quality than interfaces inside standardoptical fibers and, therefore, can be expected to introduce opticalloss. Furthermore, the capillary tube must be fabricated using a costlyfluorine-doped material, greatly increasing the expense of the coupler.

U.S. Pat. No. 7,308,173, entitled “OPTICAL FIBER COUPLER WITH LOW LOSSAND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF”, whichis hereby incorporated herein in its entirety, advantageously addressedsome of the issues discussed above by providing various embodiments ofan optical fiber coupler capable of providing a low-loss, high-couplingcoefficient interface between conventional optical fibers and opticalwaveguide devices.

Nevertheless, a number of challenges still remained. With theproliferation of multichannel optical devices (e.g., waveguide arrays),establishing low-loss high-accuracy connections to arrays of low or highNA waveguides often was problematic, especially because the spacingbetween the waveguides is very small making coupling thereto all themore difficult. U.S. Pat. No. 8,326,099, entitled “OPTICAL FIBER COUPLERARRAY”, issued Dec. 4, 2012, which is hereby incorporated herein byreference in its entirety, endeavors to address the above challenge byproviding, in at least a portion of the embodiments thereof, an opticalfiber coupler array that provides a high-coupling coefficient interfacewith high accuracy and easy alignment between an optical waveguidedevice having a plurality of closely spaced waveguides, and a pluralityof optical fibers separated by at least a fiber diameter.

U.S. Pat. No. 8,712,199, entitled “CONFIGURABLE PITCH REDUCING OPTICALFIBER ARRAY”, which is expressly incorporated by reference herein,discusses the importance of cross sectional or transverse positioningaccuracy (precise cross sectional positioning in some cases) of theindividual waveguides. Improved cross sectional positioning accuracy ofthe waveguides remains desirable.

It is also desirable to improve and/or optimize optical coupling betweena set of isolated fibers (e.g., single mode fibers) at one end andindividual modes (e.g., of a few-mode or multimode fiber) and/or cores(e.g., of a multicore fiber) at another end. Further fiber arrayimprovements can be desirable.

SUMMARY

Example embodiments described herein have innovative features, no singleone of which is indispensable or solely responsible for their desirableattributes. Without limiting the scope of the claims, some of theadvantageous features will now be summarized.

Example Set

1. An optical coupler array for optical coupling of a plurality ofoptical fibers carrying light at least at two wavelengths W-1 and W-2 toan optical device, comprising: an elongated optical element having afirst end operable to optically couple with said plurality of opticalfibers and a second end operable to optically couple with said opticaldevice,

and comprising:

-   -   a common single coupler housing structure;    -   a coupling section;    -   a plurality of longitudinal waveguides, including at least one        first waveguide and at least one second waveguide, each of said        plurality of longitudinal waveguides being positioned at a        spacing from one another, each having a capacity for at least        one optical mode of a mode field profile, and a corresponding        propagation constant, and each being embedded in said common        single housing structure, wherein at least one of said plurality        of longitudinal waveguides is a vanishing core waveguide, each        said vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-1) at said first end,        and a second inner core size (ICS-2) at said second end;    -   an outer core, longitudinally surrounding said inner core,        having a second refractive index (N-2), and having a first outer        core size (OCS-1) at said first end, and a second outer core        size (OCS-2) at said second end, and an outer cladding,        longitudinally surrounding said outer core, having a third        refractive index (N-3), a first cladding size at said first end,        and a second cladding size at said second end; and    -   wherein said common single coupler housing structure comprises a        medium having a fourth refractive index (N-4) surrounding said        plural longitudinal waveguides, wherein a relative magnitude        relationship between said first, second, third and fourth        refractive indices (N-1, N-2, N-3, and N-4, respectively),        comprises the following magnitude relationship: (N-1>N-2>N-3),        wherein a total volume of said medium of said common single        coupler housing structure is greater than a total volume of all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-1), said        first outer core size (OCS-1), and said spacing between said        plurality of longitudinal waveguides, are simultaneously and        gradually modified, in accordance with a profile, between said        first end and said second end along said optical element, until        said second inner vanishing core size (ICS-2) and said second        outer core size (OCS-2) are reached, wherein said second inner        vanishing core size (ICS-2) is selected to be insufficient to        guide light therethrough, and said second outer core size        (OCS-2) is selected to be sufficient to guide at least one        optical mode, such that:    -   light traveling from said first end to said second end escapes        from said inner vanishing core into said corresponding outer        core proximally to said second end,    -   light traveling from said second end to said first end moves        from said outer core into said corresponding inner vanishing        core proximally to said first end, and wherein, in said coupling        section located proximal to said second end, at least one said        vanishing core waveguide is in coupling distance to another said        longitudinal waveguide, said coupling distance and length of        said coupling section are configured to couple light at least at        wavelength W-1 of at least one core mode of said at least one        said vanishing core waveguide with at least one core mode of        another said longitudinal waveguide while continuing the        propagation of the light at said wavelength W-2 in said another        longitudinal waveguide.

2. The optical coupler array of Example 1, wherein proximal to saidsecond end, the light at least at wavelength W-1 and the light at saidwavelength W-2 couple into the same mode of said another longitudinalwaveguide.

3. The optical coupler array of Example 1, wherein said first innervanishing core size (ICS-1), said first outer core size (OCS-1), andsaid spacing between said plurality of longitudinal waveguides aresimultaneously and gradually reduced between said first end and saidsecond end along said optical element to said coupling section, andsimultaneously and gradually increased from said coupling section tosaid second end until said second inner vanishing core size (ICS-2) andsaid second outer core size (OCS-2) are reached.

4. The optical coupler array of Example 1, wherein said first innervanishing core size (ICS-1), said first outer core size (OCS-1), andsaid spacing between said plurality of longitudinal waveguides aresimultaneously and gradually reduced between said first end and saidsecond end along said optical element, until said second inner vanishingcore size (ICS-2) and said second outer core size (OCS-2) are reached.

5. The optical coupler array of Example 1, wherein one of thewavelengths W-1 and W-2 is signal light and the other of the wavelengthsW-1 and W-2 is pump light.

6. The optical coupler array of Example 5, wherein the signal light is1550 nm and the pump light is 980 nm.

7. The optical coupler array of Example 1, wherein one of thewavelengths W-1 and W-2 is signal light and the other of the wavelengthsW-1 and W-2 is another signal light.

8. The optical coupler array of Example 7, wherein the signal light is1550 nm and the another signal light is 1310 nm.

9. The optical coupler array of Example 1, further comprising an accessregion configured to provide access to at least one of said plurality ofwaveguides between said first and second ends.

10. The optical coupler array of Example 1, wherein said couplingsection is substantially straight.

11. The optical coupler array of Example 1, wherein said couplingsection has a neck.

12. The optical coupler array of Example 1, wherein the plurality oflongitudinal waveguides includes at least one waveguide configured tonot couple light with another of said plurality of longitudinalwaveguides in the optical coupler array.

13. A multicore fiber-wavelength division multiplexer (MCF-WDM),comprising:

-   -   a WDM-fanout device comprising a first plurality of longitudinal        waveguides, said first plurality of longitudinal waveguides        including at least one waveguide configured to propagate light        at a first wavelength and at least one waveguide configured to        propagate light at a second wavelength, wherein the WDM-fanout        device is configured to combine the light at the first        wavelength and the light at the second wavelength into a core of        a multicore fiber; and    -   a non-WDM fanout device optically coupled with the WDM-fanout        device, the non-WDM fanout device comprising a second plurality        of longitudinal waveguides, wherein each waveguide of the second        plurality of longitudinal waveguides is configured to not couple        light with another waveguide of said second plurality of        longitudinal waveguides in the non-WDM fanout device.

14. The MCF-WDM of Example 13, wherein the first plurality oflongitudinal waveguides includes at least one waveguide configured tonot couple light with another of said first plurality of longitudinalwaveguides in the WDM-fanout device.

15. The MCF-WDM of Example 13, further comprising one or more isolators,gain flattening filters, couplers, attenuators, and/or fiber Bragggratings.

16. An amplifier, comprising two of said MCF-WDMs of Example 13 and again medium therebeteween.

17. The amplifier of Example 16, wherein said gain medium is an activeMCF, said active MCF has at least one pair of nearest-neighbor cores andat least two pairs of next-nearest-neighbor cores, wherein saidnext-nearest-neighbor cores transmit light in a same direction and saidnearest-neighbor cores transmit light in the opposite direction, andwherein one of the two of said MCF-WDMs couples pump light into at leastone pair of the at least two pairs of next-nearest-neighbor cores at oneend of said active MCF, and a second of the two of said MCF-WDMs couplespump light into another pair of the at least two pairs ofnext-nearest-neighbor cores at the other end of said active MCF.

18. The amplifier of Example 16, wherein the gain medium is anErbium-doped fiber.

19. The amplifier of Example 16, further comprising a monitoringchannel.

Additional Example Set I

1. A double-tapered elongated optical coupler array, comprising:

-   -   a housing structure;    -   a first end;    -   a middle portion;    -   a second end;    -   a first tapered portion located between said first end and said        middle portion;    -   a second tapered portion located between said second end and        said middle portion, wherein said optical coupler array has an        outer diameter which is tapered up from said first end to said        middle portion and tapered down from said middle portion to said        second end; and    -   a plurality of spatial optical channels configured to optically        couple with at least one of:        -   a first multichannel optical device having a first            transverse channel pattern at said first end, or        -   a second multichannel optical device having a second            transverse channel pattern at said second end,    -   wherein the plurality of spatial optical channels comprises at        least one through-channel operable to couple at least one        optical channel of said first multichannel optical device with        at least one optical channel of said second multichannel optical        device, said at least one through-channel embedded in said        housing structure at said first and/or second ends, and    -   wherein said optical coupler array is operable to perform at        least one function of the following:        -   adaptation between dissimilar said first and second            transverse channel patterns of said first and second            multichannel optical devices, or        -   providing access to at least one optical channel of at least            one of said first or second multichannel optical device.            2. The coupler array of Example 1, wherein said at least one            through-channel is a vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-1) at said first end, a        second inner core size (ICS-2) at said second end, and an        intermediate inner core size (ICS-IN) at said middle portion        therebetween, and    -   outer longitudinal structural elements, said outer longitudinal        structural elements comprising:        -   an outer core, longitudinally surrounding said inner core,            having a second refractive index (N-2), and having a first            outer core size (OCS-1) at said first end, a second outer            core size (OCS-2) at said second end, and an intermediate            outer core size (OCS-IN) at said middle portion, and        -   an outer cladding, longitudinally surrounding said outer            core, having a third refractive index (N-3),    -   wherein a relative magnitude relationship between said first,        second, and third refractive indices (N-1, N-2, and N-3,        respectively), comprises the following magnitude relationship:        (N-1>N-2>N-3), and wherein said first inner vanishing core size        (ICS-1) and said first outer core size (OCS-1), are        simultaneously and gradually increased from said first end to        said middle portion and simultaneously and gradually reduced        from said middle portion to said second end, in accordance with        a profile along said housing structure, wherein said first and        second inner vanishing core size (ICS-1 and ICS-2, respectively)        are insufficient to guide light therethrough, and said first and        second outer core sizes (OCS-1 and OSC-2, respectively) are        sufficient to guide at least one optical mode, such that light        traveling from said first end to said middle portion couples        from said outer core to said inner vanishing core and then light        traveling from middle portion to said second end escapes from        said inner vanishing core into said outer core proximally to        said second end.        3. The coupler array of Example 1, wherein said at least one        through-channel is an enlarged core waveguide comprising:    -   an enlarged core, having a core refractive index (NCO), and        having a first enlarged core size (ECS-1) at said first end, a        second enlarged core size (ECS-2) at said second end, and an        intermediate enlarged core size (ECS-IN) at said middle portion        therebetween, and    -   an outer cladding, longitudinally surrounding said enlarged        core, having a cladding refractive index (NCL),    -   wherein a relative magnitude relationship between said        refractive indices, comprises the following magnitude        relationship: (NCO>NCL), and wherein said first enlarged core        size (ECS-1), is gradually increased from said first end to said        middle portion and gradually reduced from said middle portion to        said second end, in accordance with a profile along said housing        structure, wherein said first and second enlarged core sizes        (ECS-1 and ECS-2, respectively) and said refractive indices NCO        and NCL match waveguide properties of at least one channel of        said first and second multichannel optical devices,        respectively, and said intermediate enlarged core size (ECS-IN)        has larger mode volume than at least one channel of said first        and second multichannel optical devices, such that light        traveling from said first end to said middle portion then from        said middle portion to said second end propagates in at least        one lowest order mode.        4. The coupler array of Example 1,    -   wherein said first and second transverse channel patterns of        said first and second optical devices are dissimilar,    -   wherein said first tapered portion has a transverse channel        pattern similar to said first transverse channel pattern and        said second tapered portion has a transverse channel pattern        similar to said second transverse channel pattern,    -   wherein said first and second tapered portions each comprises:        -   a tapered housing structure,        -   a plurality of longitudinal waveguides, individual ones            positioned at a spacing from one another, individual ones            having a capacity for at least one optical mode, individual            ones embedded in said tapered housing structure proximally            to said corresponding first or second end,    -   wherein at least one of said plurality of longitudinal        waveguides is said through-channel common for both said first        and second tapered portions, and    -   wherein said housing structure comprises said first and second        tapered portions and a connecting sleeve.

-   5. The coupler array of Example 1, wherein said housing structure is    a single monolithic coupler housing structure comprising said first    tapered portion, middle portion, and second tapered portion, said    middle portion comprising an access region and comprising at least    one access optical channel comprising an optical waveguide passing    through said access region from outside space into said housing    structure operable to provide access to at least one optical channel    of at least one of said first or second multichannel optical    devices.

-   6. The coupler array of Example 5, wherein said at least one access    optical channel operable to provide access to at least one optical    channel of said first or second multichannel optical device is a    vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-1) at said first end and        an intermediate inner core size (ICS-IN) at said middle portion        therebetween, and    -   outer longitudinal structural elements, said outer longitudinal        structural elements comprising:        -   an outer core, longitudinally surrounding said inner core,            having a second refractive index (N-2), and having a first            outer core size (OCS-1) at said first end and an            intermediate outer core size (OCS-IN) at said middle            portion, and        -   an outer cladding, longitudinally surrounding said outer            core, having a third refractive index (N-3),    -   wherein a relative magnitude relationship between said first,        second, and third refractive indices (N-1, N-2, and N-3,        respectively), comprises the following magnitude relationship:        (N-1>N-2>N-3), and wherein said first inner vanishing core size        (ICS-1) and said first outer core size (OCS-1), are        simultaneously and gradually increased from said first end to        said middle portion, in accordance with a profile along said        optical housing structure, wherein said first inner vanishing        core size (ICS-1) is insufficient to guide light therethrough,        and said first outer core size (OCS-1) is sufficient to guide at        least one optical mode, such that light traveling from said        first end to said middle portion couples from said outer core to        said inner vanishing core.

-   7. The coupler array of Example 6, wherein said at least one access    optical channel also comprises a standard optical fiber fusion    spliced to said vanishing core waveguide with the splice location    outside said housing structure in such a way that said vanishing    core waveguide passes through said access region from outside space    into said housing structure.

-   8. The coupler array of Example 6, wherein said at least one access    optical channel also comprises a standard optical fiber fusion    spliced to said vanishing core waveguide with the splice location    inside said housing structure in such a way that said standard    optical fiber passes through said access region from outside space    into said housing structure.

-   9. The coupler array of Example 1, wherein said first and second    multichannel optical devices are multicore fibers connected to said    housing structure at both said first and second ends.

-   10. The coupler array of Example 5, wherein said first and second    multichannel optical devices are two ends of the same span of a    multicore fiber having a circumferential core arrangement pattern,    numbered along the circumference 1, 2, . . . N, wherein a connection    orientation at said first end provides coupling of said at least one    access optical channel to core number 1, and a connection    orientation at said second end provides coupling of the core number    1 via said at least one through-channel to the core number 2 at said    first end, core number 2 couples to core number 3, until core number    N-1 is coupled to core number N, which is coupled to a second of    said at least one access optical channel at said second end.

-   11. The optical coupler array of Example 1,    -   wherein said plurality of spatial optical channels disposed        within the housing structure forms a first transverse channel        pattern at the first end and a second transverse channel pattern        at the second end, wherein the second transverse channel pattern        is different from the first transverse channel pattern.

-   12. The optical coupler array of Example 1, further comprising:    -   an optical fiber have a first end disposed within the housing        structure and a second end disposed outside the housing        structure.

-   13. The optical coupler array of Example 12, wherein the first end    of the optical fiber is disposed at the first or second end of the    housing structure.

-   14. The optical coupler array of Example 12, wherein the optical    fiber exits the housing structure through the middle portion of the    housing structure.

-   15. The optical coupler array of Example 12, wherein the optical    fiber comprises two optical fibers, wherein the first end of one of    the optical fibers is disposed at the first end of the housing    structure and the first end of the other one of the optical fibers    is disposed at the second end of the housing structure.

-   16. The optical coupler array of Example 1, wherein the middle    portion is bent from 90° to 170°.

-   17. The optical coupler array of Example 1, wherein the at least one    through-channel does not include a splice within the housing    structure.

-   18. The coupler array of Example 1, wherein at least one of said    first or second multichannel optical device has at least one    multimode optical channel.

-   19. The coupler array of Example 18, wherein said multimode optical    channel is an inner cladding of a double-clad multicore fiber.

-   20. The coupler array of Example 5, wherein both of said first and    second multichannel optical devices are multicore fibers and cores    of said multicore fibers are coupled via through-channels and said    at least one access optical channel is a multimode fiber coupled to    cladding modes of said inner cladding of a double-clad multicore    fiber.

Additional Example Set II

-   1. A double-tapered elongated optical coupler array comprising:    -   a housing structure,    -   a first end,    -   a middle portion,    -   a second end,    -   a first tapered portion located between said first end and said        middle portion, and    -   a second tapered portion located between said second end and        said middle portion, and    -   having an outer diameter which is tapered up from said first end        to said middle portion and tapered down from said middle portion        to said second end and comprising    -   a plurality of spatial optical channels configured to optically        couple with at least one of:    -   a first multichannel optical device having a first transverse        channel pattern at said first end and    -   a second multichannel optical device having a second transverse        channel pattern at said second end, and    -   at least one through-channel operable to directly couple at        least one optical channel of said first multichannel optical        device with at least one optical channel of said second        multichannel optical device, said at least one through-channel        embedded in said housing structure at said both first and second        ends, and    -   said optical coupler array operable to perform at least one        function of the following:    -   adaptation between dissimilar said first and second transverse        channel patterns of said first and second optical devices, and    -   providing direct access to at least one optical channel of at        least one of said first or second multichannel optical devices.-   2. The coupler array of Example 1 wherein said at least one    through-channel is a vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-1) at said first end, a        second inner core size (ICS-2) at said second end, and an        intermediate inner core size (ICS-IN) at said middle portion        therebetween, and outer longitudinal structural elements, said        outer longitudinal structural elements comprising:        -   an outer core, longitudinally surrounding said inner core,            having a second refractive index (N-2), and having a first            outer core size (OCS-1) at said first end, a second outer            core size (OCS-2) at said second end, and an intermediate            outer core size (OCS-IN) at said middle portion, and an            outer cladding, longitudinally surrounding said outer core,            having a third refractive index (N-3),    -   wherein a relative magnitude relationship between said first,        second, and third refractive indices (N-1, N-2, and N-3,        respectively), comprises the following magnitude relationship:        (N-1>N-2>N-3), and wherein said first inner vanishing core size        (ICS-1) and said first outer core size (OCS-1), are        simultaneously and gradually increased from said first end to        said middle portion and simultaneously and gradually reduced        from said middle portion to said second end, in accordance with        a predetermined profile along said housing structure, wherein        said first and second inner vanishing core size (ICS-1 and        ICS-2, respectively) are selected to be insufficient to guide        light therethrough, and said first and second outer core sizes        (OCS-1 and OSC-2, respectively) are selected to be sufficient to        guide at least one optical mode, such that light traveling from        said first end to said middle portion couples from said outer        core to said inner vanishing core and then light traveling from        middle portion to said second end escapes from said inner        vanishing core into said outer core proximally to said second        end.-   3. The coupler array of Example 1 wherein said at least one    through-channel is an enlarged core waveguide comprising:    -   an enlarged core, having a core refractive index (NCO), and        having a first enlarged core size (ECS-1) at said first end, a        second enlarged core size (ECS-2) at said second end, and an        intermediate enlarged core size (ECS-IN) at said middle portion        therebetween, and    -   an outer cladding, longitudinally surrounding said enlarged        core, having a cladding refractive index (NCL),    -   wherein a relative magnitude relationship between said        refractive indices, comprises the following magnitude        relationship: (NCO>NCL), and wherein said first enlarged core        size (ECS-1), is gradually increased from said first end to said        middle portion and gradually reduced from said middle portion to        said second end, in accordance with a predetermined profile        along said housing structure, wherein said first and second        enlarged core sizes (ECS-1 and ECS-2, respectively) and said        refractive indices NCO and NCL are selected to match waveguide        properties of at least one channel of said first and second        multichannel optical devices, respectively, and said        intermediate enlarged core size (ECS-IN) is selected to have        larger mode volume than at least one channel of said first and        second multichannel optical devices, such that light traveling        from said first end to said middle portion then from middle        portion to said second end keeps propagating in at least one        lowest order mode.-   4. The coupler array of Example 2 or 3 wherein    -   said first and second transverse channel patterns of said first        and second optical devices are dissimilar,    -   said first tapered portion has a transverse channel pattern        similar to said first transverse channel pattern and said second        tapered portion has a transverse channel pattern similar to said        second transverse channel pattern, and    -   said first and second tapered portions each comprises:        -   a tapered housing structure,        -   a plurality of longitudinal waveguides each positioned at a            predetermined spacing from one another, each having a            capacity for at least one optical mode of a predetermined            mode field profile, each embedded in said tapered housing            structure proximally to said corresponding first or second            end,        -   wherein at least one of said plurality of longitudinal            waveguides is said through-channel common for both said            first and second tapered portions, and wherein    -   said housing structure comprises said first and second tapered        portions and a connecting sleeve.-   5. The coupler array of Example 2 or 3 wherein said housing    structure is a single monolithic coupler housing structure    comprising    -   said first tapered portion,    -   middle portion, and    -   second tapered portion,        -   said middle portion comprising an access region    -   and comprising at least one direct access optical channel        comprising an optical waveguide passing through said access        region from outside space into said housing structure operable        to providing direct access to at least one optical channel of at        least one of said first or second multichannel optical devices.-   6. The coupler array of Example 5 wherein said at least one direct    access optical channel operable to providing direct access to at    least one optical channel of said first multichannel optical device    is a direct access vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-1) at said first end and        an intermediate inner core size (ICS-IN) at said middle portion        therebetween, and    -   outer longitudinal structural elements, said outer longitudinal        structural elements comprising:        -   an outer core, longitudinally surrounding said inner core,            having a second refractive index (N-2), and having a first            outer core size (OCS-1) at said first end and an            intermediate outer core size (OCS-IN) at said middle            portion, and an outer cladding, longitudinally surrounding            said outer core, having a third refractive index (N-3),    -   wherein a relative magnitude relationship between said first,        second, and third refractive indices (N-1, N-2, and N-3,        respectively), comprises the following magnitude relationship:        (N-1>N-2>N-3), and wherein said first inner vanishing core size        (ICS-1) and said first outer core size (OCS-1), are        simultaneously and gradually increased from said first end to        said middle portion, in accordance with a predetermined profile        along said optical housing structure, wherein said first inner        vanishing core size (ICS-1) is selected to be insufficient to        guide light therethrough, and said first outer core size (OCS-1)        is selected to be sufficient to guide at least one optical mode,        such that light traveling from said first end to said middle        portion couples from said outer core to said inner vanishing        core.-   7. The coupler array of Example 6 wherein said at least one direct    access optical channel also comprises a standard optical fiber    fusion spliced to said direct access vanishing core waveguide with    the splice location outside said housing structure in such a way    that said direct access vanishing core waveguide passes through said    access region from outside space into said housing structure.-   8. The coupler array of Example 6 wherein said at least one direct    access optical channel also comprises a standard optical fiber    fusion spliced to said direct access vanishing core waveguide with    the splice location inside said housing structure in such a way that    said standard optical fiber passes through said access region from    outside space into said housing structure.-   9. The coupler array of Example 1 wherein said first and second    multichannel optical devices are multicore fibers connected to said    housing structure at both said first and second ends.-   10. The coupler array of Example 5 wherein said first and second    multichannel optical devices are two ends of the same span of a    multicore fiber having a circumferential core arrangement pattern,    for example, numbered along the circumference 1, 2, . . . N, wherein    a connection orientation at said first end provides coupling of said    at least one direct access optical channel to core number 1, and a    connection orientation at said second end provides coupling of the    core number 1 via said at least one through-channel to the core    number 2 at said first end, core number 2 couples to core number 3    and so on, until core number N-1 is coupled to core number N, which    is finally coupled to second of said at least one direct access    optical channel at said second end.-   11. An optical coupler array comprising:    -   a housing comprising:        -   a first end,        -   a second end,        -   a middle portion therebetween,        -   a first tapered portion located between said first end and            said middle portion, and        -   a second tapered portion located between said second end and            said middle portion; and    -   a plurality of spatial optical channels disposed within the        housing forming a first transverse channel pattern at the first        end and a second transverse channel pattern at the second end,        wherein the second transverse channel pattern is different from        the first transverse channel pattern.-   12. An optical coupler array comprising:    -   a housing comprising:        -   a first end,        -   a second end,        -   a middle portion therebetween,        -   a first tapered portion located between said first end and            said middle portion, and        -   a second tapered portion located between said second end and            said middle portion;    -   a plurality of spatial optical channels disposed within the        housing forming a first transverse channel pattern at the first        end and a second transverse channel pattern at the second end;        and    -   an optical fiber have a first end disposed within the housing        and a second end disposed outside the housing.-   13. The optical coupler array of Example 12, wherein the first end    of the optical fiber is disposed at the first or second end of the    housing.-   14. The optical coupler array of Example 12 or 13, wherein the    optical fiber exits the housing through the middle portion of the    housing.-   15. The optical coupler array of any of Examples 12-14, wherein the    optical fiber comprises two optical fibers, wherein the first end of    one of the optical fibers is disposed at the first end of the    housing and the first end of the other one of the optical fibers is    disposed at the second end of the housing.-   16. The optical coupler array of any of Examples 12-15, wherein the    optical fiber comprises an add and/or drop channel.-   17. The optical coupler array of any of Examples 12-16, wherein the    second transverse channel pattern is different from the first    transverse channel pattern.-   18. The optical coupler array of any of Examples 11-17, wherein the    plurality of spatial optical channels comprises a vanishing core    waveguide.-   19. The optical coupler array of any of Examples 11-18, wherein the    plurality of spatial optical channels comprises an enlarged core    waveguide.-   20. The optical coupler array of any of Examples 11-19, wherein the    array forms a gyroscope.-   21. The optical coupler array of any Examples 11-20, wherein    individual ones of the spatial optical channels do not include    splices within the housing.-   22. The optical coupler array of any of Examples 11-21, wherein the    middle portion is bent from 90° to 170°.-   23. The optical coupler array of any of Examples 1-10, wherein the    at least one through-channel does not include a splice within the    housing structure.-   24. The optical coupler array of any of Examples 1-10 or 23, wherein    the middle portion is bent from 90° to 170°.-   25. The coupler array of Example 1 wherein at least one of said    first or second multichannel optical device has at least one    multimode optical channel.-   26. The coupler array of Example 25 wherein said multimode optical    channel is an inner cladding of a double-clad multicore fiber.-   27. The coupler array of Example 26 wherein said direct access is    provided to at least one optical mode of said multimode optical    channel.-   28. The coupler array of Example 27 and Example 5 wherein both of    said first and second multichannel optical devices are multicore    fibers and cores of said multicore fibers are coupled via    through-channels and said at least one direct access optical channel    is a multimode fiber coupled to cladding modes of said inner    cladding of a double-clad multicore fiber.-   29. The coupler array of Example 12, wherein the optical fiber is a    multimode fiber configured to provide access to a multimode optical    channel.-   30. The coupler array of Example 29, wherein the multimode optical    channel is an inner cladding of a double-clad multicore fiber.

Additional Example Set III

1. A multichannel optical coupler array for optical coupling of aplurality of optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:        -   a common single coupler housing structure; a plurality of            longitudinal waveguides each positioned at a predetermined            spacing from one another, each having a capacity for at            least one optical mode of a predetermined mode field            profile, each embedded in said common single housing            structure proximally to said second end, wherein at, least            one of said plural longitudinal waveguides is a vanishing            core waveguide, each said at least one vanishing core            waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, and a second inner core size (ICS-2) at                said second end; an outer core, longitudinally                surrounding said inner core, having a second refractive                index (N-2), and having a first outer core size (OCS-I)                at said first end, and a second outer core size (OCS-2)                at said second end, and an outer cladding,                longitudinally surrounding said outer core, having a                third refractive index (N-3), a first cladding size at                said first end, and a second cladding size at said                second end; and wherein said common single coupler                housing structure comprises a transversely contiguous                medium having a fourth refractive index (N-4)                surrounding said plural longitudinal waveguides, wherein                a predetermined relative magnitude relationship between                said first, second, third and fourth refractive indices                (N-1, N-2, N-3, and N-4, respectively), comprises the                following magnitude relationship: (N-1>N-2>N-3),    -   wherein a total volume of said medium or said common single        coupler housing structure, is greater than a total volume or all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-I), said        first outer core size (OCS-I), and said predetermined spacing        between said plural longitudinal waveguides, are simultaneously        and gradually reduced, in accordance with a predetermined        reduction profile, between said first end and said second end        along said optical element, until said second inner vanishing        core size (ICS-2) and said second outer core size (OCS-2) are        reached, wherein said second inner vanishing core size (ICS-2)        is selected to be insufficient to guide light therethrough, and        said second outer core size (OCS-2) is selected to be sufficient        to guide at least one optical mode, such that:        -   light traveling from said first end to said second end            escapes from said inner vanishing core into said            corresponding outer core proximally to said second end, and            light traveling from said second end to said first end moves            from said outer core into said corresponding inner vanishing            core proximally to said first end,    -   and wherein said common single coupler housing structure        proximally to said first end has one of the following cross        sectional configurations: a ring surrounding said plurality of        longitudinal waveguides, a transversely contiguous structure        with plurality of holes, wherein at least one said hole contains        at least one of said plurality of longitudinal waveguides.

2. A multichannel optical coupler array, comprising:

-   -   an elongated optical element having a first end and a second        end, wherein said first and second ends are operable to        optically couple with a plurality of optical fibers, an optical        device, or combinations thereof, the optical element further        comprising:        -   a coupler housing structure; and        -   a plurality of longitudinal waveguides arranged with respect            to one another, each having a capacity for at least one            optical mode, the plurality of longitudinal waveguides            embedded in said housing structure, wherein said plurality            of longitudinal waveguides comprises at least one vanishing            core waveguide, each said at least one vanishing core            waveguide, said at least one vanishing core waveguide            comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having an inner core size;            -   an outer core, longitudinally surrounding said inner                core, having a second refractive index (N-2), and having                an outer core size; and            -   an outer cladding, longitudinally surrounding said outer                core, having a third refractive index (N-3), and having                a cladding size;    -   wherein said coupler housing structure comprises a medium having        a fourth refractive index (N-4) surrounding said plurality of        longitudinal waveguides, wherein N-1>N-2>N-3,    -   wherein said inner core size, said outer core size, and spacing        between said plurality of longitudinal waveguides reduces along        said optical element from said first end to said second end such        that at said second end, said inner core size is insufficient to        guide light therethrough, and said outer core size is sufficient        to guide at least one optical mode, and    -   wherein said coupler housing structure at a proximity to the        first end has one of the following cross sectional        configurations: a ring surrounding said plurality of        longitudinal waveguides with a gap between said ring and said        plurality of longitudinal waveguides, or a structure with a        plurality of holes, at least one hole containing at least one of        said plurality of longitudinal waveguides.

3. The optical coupler array of example 2, wherein the coupler housingstructure comprises a common single coupler housing structure.

4. The optical coupler array of any of the preceding examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesextends outside the coupler housing structure.

5. The optical coupler array of any of the preceding examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed within the coupler housing structure and does not extendsbeyond the coupler housing structure.

6. The optical coupler array of any of the preceding examples, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed at an outer cross sectional boundary region of the couplerhousing structure and does not extends beyond the coupler housingstructure.

7. The optical coupler array of any of Examples 2-6, wherein the mediumis a transversely contiguous medium.

8. The optical coupler array of any of Examples 2-7, wherein a totalvolume of said medium of said coupler housing structure is greater thana total volume of all the inner and outer cores of the at least onevanishing core waveguide confined within said coupler housing structure.

9. The optical coupler array of any of Examples 2-8, wherein said innercore size, said outer core size, and spacing between said plurality oflongitudinal waveguides simultaneously and gradually reduces from saidfirst end to said second end.

10. The optical coupler array of any of the preceding examples, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.

11. The optical coupler array of any of the preceding examples, whereinthe one of the cross sectional configurations is the ring surroundingsaid plurality of longitudinal waveguides.

12. The optical coupler array of Example 11, wherein the plurality oflongitudinal waveguides are in a hexagonal arrangement.

13. The optical coupler array of any of Examples 11-12, wherein the ringhas a circular inner cross section.

14. The optical coupler array of any of Examples 11-12, wherein the ringhas a non-circular inner cross section.

15. The optical coupler array of Example 14, wherein the inner crosssection is hexagonal.

16. The optical coupler array of Example 14, wherein the inner crosssection is D-shaped.

17. The optical coupler array of any of Examples 11-16, wherein the ringhas a circular outer cross section.

18. The optical coupler array of any of Examples 11-16, wherein the ringhas a non-circular outer cross section.

19. The optical coupler array of Example 18, wherein the outer crosssection is hexagonal.

20. The optical coupler array of Example 18, wherein the outer crosssection is D-shaped.

21. The optical coupler array of any of Examples 1-10, wherein the oneof the cross sectional configurations is the structure with theplurality of holes.

22. The optical coupler array of Example 21, wherein the holes are in ahexagonal arrangement.

23. The optical coupler array of Example 21, wherein the holes are in arectangular arrangement.

24. The optical coupler array of Example 21, wherein said plurality ofholes is defined in an XY array.

25. The optical coupler array of any of Examples 21-24, wherein at leastone hole comprises non-waveguide material.

26. The optical coupler array of any of Examples 21-25, wherein at leastone hole has a circular cross section.

27. The optical coupler array of any of Examples 21-26, wherein at leastone hole has a non-circular cross section.

28. The optical coupler array of Example 27, wherein the non-circularcross section is D-shaped.

29. The optical coupler array of any of Examples 21-28, wherein at leastone of the holes has a different dimension than another one of theholes.

30. The optical coupler array of any of Examples 21-29, wherein at leastone of the holes has a different shape than another one of the holes.

31. The optical coupler array of any of Examples 21-30, wherein theholes are isolated.

32. The optical coupler array of any of Examples 21-30, wherein some ofthe holes are connected.

33. The optical coupler array of any of the preceding examples, whereinthe at least one vanishing core waveguide comprises a single mode fiber.

34. The optical coupler array of any of the preceding examples, whereinthe at least one vanishing core waveguide comprises a multi-mode fiber.

35. The optical coupler array of any of the preceding examples, whereinthe at least one vanishing core waveguide comprises a polarizationmaintaining fiber.

36. A multichannel optical coupler array, comprising:

-   -   an elongated optical element having a first end and a second        end, wherein said first and second ends are operable to        optically couple with a plurality of optical fibers, an optical        device, or combinations thereof, the optical element further        comprising:        -   a coupler housing structure; and        -   a plurality of longitudinal waveguides arranged with respect            to one another, each having a capacity for at least one            optical mode, the plurality of longitudinal waveguides            embedded in said housing structure, wherein said plurality            of longitudinal waveguides comprises at least one vanishing            core waveguide, each said at least one vanishing core            waveguide, said at least one vanishing core waveguide            comprising:            -   an inner vanishing core having a first refractive index                (N-1), and having an inner core size;            -   an outer core, longitudinally surrounding said inner                core, having a second refractive index (N-2) and having                an outer core size; and            -   an outer cladding, longitudinally surrounding said outer                core, having a third refractive index (N-3), and having                a cladding size;    -   wherein said coupler housing structure comprises a medium having        a fourth refractive index (N-4) surrounding said plurality of        longitudinal waveguides, wherein N-1>N-2>N-3,    -   wherein said inner core size, said outer core size, and spacing        between said plurality of longitudinal waveguides reduces along        said elongated optical element from said first end to said        second end such that at said second end, said inner core size is        insufficient to guide light therethrough, and said outer core        size is sufficient to guide at least one optical mode, and    -   wherein said coupler housing structure at a proximity to the        first end has a cross sectional configuration comprising at        least one hole, the at least one hole containing at least one of        said plurality of longitudinal waveguides, wherein the hole is        larger than the at least one of said plurality of longitudinal        waveguides such that the at least one of said plurality of        longitudinal waveguides is movable with respect to the coupler        housing structure in a lateral direction.

37. The optical coupler array of Example 36, wherein the coupler housingstructure comprises a common single coupler housing structure.

38. The optical coupler array of any of Examples 36-37, whereinproximate the first end, one of the plurality of longitudinal waveguidesextends outside the coupler housing structure.

39. The optical coupler array of any of Examples 36-38, whereinproximate the first end, one of the plurality of longitudinal waveguidesis disposed within the coupler housing structure.

40. The optical coupler array of any of Examples 36-39, wherein themedium is a transversely contiguous medium.

41. The optical coupler array of any of Examples 36-40, wherein a totalvolume of said medium of said coupler housing structure is greater thana total volume of all the inner and outer cores of the at least onevanishing core waveguide confined within said coupler housing structure.

42. The optical coupler array of any of Examples 36-41, wherein saidinner core size, said outer core size, and spacing between saidplurality of longitudinal waveguides simultaneously and graduallyreduces from said first end to said second end.

43. The optical coupler array of any of Examples 36-42, whereinproximate the second end, the coupler array comprises substantially nogap between the coupler housing structure and the plurality oflongitudinal waveguides.

44. The optical coupler array of any Examples 36-43, wherein the atleast one hole comprises a single hole and the at least one of saidplurality of longitudinal waveguides comprises a plurality oflongitudinal waveguides.

45. The optical coupler array of Example 44, wherein the plurality oflongitudinal waveguides are in a hexagonal arrangement.

46. The optical coupler array of any of Examples 44-45, wherein thesingle hole as a circular cross section.

47. The optical coupler array of any of Examples 44-45, wherein thesingle hole has a non-circular cross section.

48. The optical coupler array of Example 47, wherein the non-circularcross section is hexagonal.

49. The optical coupler array of Example 47, wherein the non-circularcross section is D-shaped.

50. The optical coupler array of any of Examples 44-49, wherein thecoupler housing structure has a circular outer cross section.

51. The optical coupler array of any of Examples 44-49, wherein thecoupler housing structure has a non-circular outer cross section.

52. The optical coupler array of Example 51, wherein the outer crosssection is hexagonal.

53. The optical coupler array of Example 51, wherein the outer crosssection is D-shaped.

54. The optical coupler array of any of Examples 36-43, wherein the atleast one hole comprises a plurality of holes.

55. The optical coupler array of Example 54, wherein the plurality ofholes are in a hexagonal arrangement.

56. The optical coupler array of Example 54, wherein the plurality ofholes are in a rectangular arrangement.

57. The optical coupler array of Example 54, wherein said plurality ofholes is defined by an XY array.

58. The optical coupler array of any of Examples 54-57, wherein one ormore of the plurality of holes comprises non-waveguide material.

59. The optical coupler array of any of Examples 54-58, wherein one ormore of the plurality of holes has a circular cross section.

60. The optical coupler array of any of Examples 54-59, wherein one ormore of the plurality of holes has a non-circular cross section.

61. The optical coupler array of Example 60, wherein the non-circularcross section is D-shaped.

62. The optical coupler array of any of Examples 54-61, wherein one ormore of the plurality of holes has a different dimension than anotherone of the holes.

63. The optical coupler array of any of Examples 54-62, wherein one ormore of the plurality of holes has a different shape than another one ofthe holes.

64. The optical coupler array of any of Examples 54-63, wherein theholes are isolated.

65. The optical coupler array of any of Examples 54-63, wherein some ofthe holes are connected.

66. The optical coupler array of any of Examples 54-65, wherein the atleast one vanishing core waveguide comprises a single mode fiber.

67. The optical coupler array of any of Examples 54-66, wherein the atleast one vanishing core waveguide comprises a multi-mode fiber.

68. The optical coupler array of any of Examples 54-67, wherein the atleast one vanishing core waveguide comprises a polarization maintainingfiber.

Additional Example Set IV

1. A multichannel optical coupler array for optical coupling a pluralityof optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:    -   a common single coupler housing structure; a plurality of        longitudinal waveguides each positioned at a predetermined        spacing from one another, each having a capacity for at least        one optical mode of a predetermined mode field profile, each        embedded in said common single housing structure, wherein at,        least one of said plural longitudinal waveguides is a vanishing        core waveguide, each said at least one vanishing core waveguide        comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-I) at said first end,        and a second inner core size (ICS-2) at said second end; an        outer core, longitudinally surrounding said inner core, having a        second refractive index (N-2), and having a first outer core        size (OCS-I) at said first end, and a second outer core size        (OCS-2) at said second end, and an outer cladding,        longitudinally surrounding said outer core, having a third        refractive index (N-3), a first cladding size at said first end,        and a second cladding size at said second end; and wherein said        common single coupler housing structure comprises a transversely        contiguous medium having a fourth refractive index (N-4)        surrounding said plural longitudinal waveguides, wherein a        predetermined relative magnitude relationship between said        first, second, third and fourth refractive indices (N-1, N-2,        N-3, and N-4, respectively), comprises the following magnitude        relationship: (N-1>N-2>N-3),    -   wherein a total volume of said medium or said common single        coupler housing structure, is greater than a total volume or all        said vanishing core waveguides inner cores and said outer cores        confined within said common single coupler housing structure,        and wherein said first inner vanishing core size (ICS-I), said        first outer core size (OCS-I), and said predetermined spacing        between said plural longitudinal waveguides, are simultaneously        and gradually reduced, in accordance with a predetermined        reduction profile, between said first end and said second end        along said optical element, until said second inner vanishing        core size (ICS-2) and said second outer core size (OCS-2) are        reached, wherein said second inner vanishing core size (ICS-2)        is selected to be insufficient to guide light therethrough, and        said second outer core size (OCS-2) is selected to be sufficient        to guide at least one optical mode, such that:    -   light traveling from said first end to said second end escapes        from said inner vanishing core into said corresponding outer        core proximally to said second end, and light traveling from        said second end to said first end moves from said outer core        into said corresponding inner vanishing core proximally to said        first end, and wherein said common single coupler housing        structure at a close proximity to the first end has one of the        following cross sectional configurations: a ring surrounding        said plurality of longitudinal waveguides, a contiguous        structure with plurality of holes, at least one hole containing        at least one of said plurality of longitudinal waveguides.        2. A multichannel optical coupler array for optical coupling a        plurality of optical fibers to an optical device, comprising:    -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers and a second        end operable to optically couple with said optical device, and        comprising:    -   a coupler housing structure; a plurality of longitudinal        waveguides each positioned at a spacing from one another, each        having a capacity for at least one optical mode, each embedded        in said housing structure, wherein at, least one of said plural        longitudinal waveguides is a vanishing core waveguide, each said        at least one vanishing core waveguide comprising:    -   an inner vanishing core, having a first refractive index (N-1),        and having a first inner core size (ICS-I) at said first end,        and a second inner core size (ICS-2) at said second end; an        outer core, longitudinally surrounding said inner core, having a        second refractive index (N-2), and having a first outer core        size (OCS-I) at said first end, and a second outer core size        (OCS-2) at said second end, and an outer cladding,        longitudinally surrounding said outer core, having a third        refractive index (N-3), a first cladding size at said first end,        and a second cladding size at said second end; and wherein said        coupler housing structure comprises a medium having a fourth        refractive index (N-4) surrounding said plural longitudinal        waveguides, wherein a relative magnitude relationship between        said first, second, third and fourth refractive indices (N-1,        N-2, N-3, and N-4, respectively), comprises the following        magnitude relationship: (N-1>N-2>N-3),    -   wherein said first inner vanishing core size (ICS-I), said first        outer core size (OCS-I), and said spacing between said plural        longitudinal waveguides, reduces between said first end and said        second end along said optical element, until said second inner        vanishing core size (ICS-2) and said second outer core size        (OCS-2) are reached, wherein said second inner vanishing core        size (ICS-2) is insufficient to guide light therethrough, and        said second outer core size (OCS-2) is sufficient to guide at        least one optical mode, such that: light traveling from said        first end to said second end escapes from said inner vanishing        core into said corresponding outer core proximally to said        second end, and light traveling from said second end to said        first end moves from said outer core into said corresponding        inner vanishing core proximally to said first end, and wherein        said coupler housing structure at a close proximity to the first        end has one of the following cross sectional configurations: a        ring surrounding said plurality of longitudinal waveguides, or a        structure with plurality of holes, at least one hole containing        at least one of said plurality of longitudinal waveguides.

Additional Example Set V

1. A multichannel optical coupler array for optical coupling of aplurality of optical fibers to an optical device, comprising:

-   -   an elongated optical element having a first end operable to        optically couple with said plurality optical fibers, an        intermediate cross section, and a second end operable to        optically couple with said optical device, and comprising:        -   a common single coupler housing structure; a plurality of            longitudinal waveguides each positioned at a predetermined            spacing from one another, each having a capacity for at            least one optical mode of a predetermined mode field            profile, each embedded in said common single housing            structure proximally to said second end, wherein at least            one of said plural longitudinal waveguides is a vanishing            core waveguide, each said at least one vanishing core            waveguide comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, an intermediate inner core size (ICS-IN)                at said intermediate cross section, and a second inner                core size (ICS-2) at said second end; an outer core,                longitudinally surrounding said inner core, having a                second refractive index (N-2), and having a first outer                core size (OCS-I) at said first end, an intermediate                outer core size (OCS-IN) at said intermediate cross                section, and a second outer core size (OCS-2) at said                second end, and an outer cladding, longitudinally                surrounding said outer core, having a third refractive                index (N-3), a first cladding size at said first end,                and a second cladding size at said second end; and                wherein said common single coupler housing structure                comprises a transversely contiguous medium having a                fourth refractive index (N-4) surrounding said plural                longitudinal waveguides, wherein a predetermined                relative magnitude relationship between said first,                second, third and fourth refractive indices (N-1, N-2,                N-3, and N-4, respectively), comprises the following                magnitude relationship: (N-1>N-2>N-3), wherein a total                volume of said medium or said common single coupler                housing structure, is greater than a total volume or all                said vanishing core waveguides inner cores and said                outer cores confined within said common single coupler                housing structure, and wherein said first inner                vanishing core size (ICS-I), said first outer core size                (OCS-I), and said predetermined spacing between said                plural longitudinal waveguides, are simultaneously and                gradually reduced, in accordance with a predetermined                reduction profile, between said first end and said                second end along said optical element, until said second                inner vanishing core size (ICS-2) and said second outer                core size (OCS-2) are reached, wherein said intermediate                inner vanishing core size (ICS-IN) is selected to be                insufficient to guide light therethrough, and said                intermediate outer core size (OCS-IN) is selected to be                sufficient to guide at least one optical mode, and said                second outer core size (OCS-2) is selected to be                insufficient to guide light therethrough such that:            -   light traveling from said first end to said second end                escapes from said inner vanishing core into said                corresponding outer core proximally to said intermediate                cross section, and escapes from said outer core into a                combined waveguide formed by at least two neighboring                outer cores proximally to said second end, and            -   at least one waveguide mode of light traveling from said                second end to said first end moves from the combined                waveguide formed by at least two neighboring outer cores                into said outer core proximally to said intermediate                cross section, and moves from said outer core into said                corresponding inner vanishing core proximally to said                first end,    -   and wherein said common single coupler housing structure        proximally to said first end has a cross sectional configuration        comprising a transversely contiguous structure with at least one        hole, wherein the at least one hole contains at least one of        said plurality of longitudinal waveguides creating a gap between        the coupler housing structure and the at least one of said        plurality of longitudinal waveguides.

2. A multichannel optical coupler array comprising:

-   -   an elongated optical element having a first end, an intermediate        cross section, and a second end, and comprising:        -   a coupler housing structure; a plurality of longitudinal            waveguides each positioned at a spacing from one another,            each having a capacity for at least one optical mode, each            disposed in said housing structure, wherein at least one of            said plural longitudinal waveguides is a vanishing core            waveguide, each said at least one vanishing core waveguide            comprising:            -   an inner vanishing core, having a first refractive index                (N-1), and having a first inner core size (ICS-I) at                said first end, an intermediate inner core size (ICS-IN)                at said intermediate cross section, and a second inner                core size (ICS-2) at said second end; an outer core,                longitudinally surrounding said inner core, having a                second refractive index (N-2), and having a first outer                core size (OCS-I) at said first end, an intermediate                outer core size (OCS-IN) at said intermediate cross                section, and a second outer core size (OCS-2) at said                second end, and an outer cladding, longitudinally                surrounding said outer core, having a third refractive                index (N-3), a first cladding size at said first end,                and a second cladding size at said second end; and                wherein said coupler housing structure comprises a                medium having a fourth refractive index (N-4)                surrounding said plural longitudinal waveguides, wherein                a relative magnitude relationship between said first,                second, third and fourth refractive indices (N-1, N-2,                N-3, and N-4, respectively), comprises the following                magnitude relationship: (N-1>N-2>N-3), and wherein said                first inner vanishing core size (ICS-I), said first                outer core size (OCS-I), and said spacing between said                plural longitudinal waveguides are reduced between said                first end and said second end along said optical                element, wherein said intermediate inner vanishing core                size (ICS-IN) is insufficient to guide light                therethrough, and said intermediate outer core size                (OCS-IN) is sufficient to guide at least one optical                mode, and said second outer core size (OCS-2) is                insufficient to guide light therethrough such that:            -   light traveling from said first end to said second end                escapes from said inner vanishing core into said                corresponding outer core proximally to said intermediate                cross section, and escapes from said outer core into a                combined waveguide formed by at least two neighboring                outer cores proximally to said second end, and            -   at least one waveguide mode of light traveling from said                second end to said first end moves from the combined                waveguide formed by at least two neighboring outer cores                into said outer core proximally to said intermediate                cross section, and moves from said outer core into said                corresponding inner vanishing core proximally to said                first end.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote correspondingor similar elements throughout the various figures:

FIG. 1A is a schematic diagram of a side view of a first exampleembodiment of an optical fiber coupler array, which comprises at leastone vanishing core waveguide (VC waveguide), illustrated therein by wayof example as a single VC waveguide, and at least one Non-VC waveguide,illustrated therein by way of example as a plurality of Non-VCwaveguides, disposed symmetrically proximally to the example single VCwaveguide;

FIG. 1B is a schematic diagram of a side view of a second exampleembodiment of an optical fiber coupler array, which comprises at leastone vanishing core waveguide (VC waveguide), illustrated therein by wayof example as a single VC waveguide, and at least one Non-VC waveguide,illustrated therein by way of example as a single Non-VC waveguide,disposed in parallel proximity to the example single VC waveguide, wherea portion of the optical fiber coupler array has been configured tocomprise a higher channel-to-channel spacing magnitude at its second(smaller) end than the corresponding channel-to-channel spacingmagnitude at the second end of the optical fiber coupler array of FIG.1A;

FIG. 1C is a schematic diagram of a side view of a third exampleembodiment of an optical fiber coupler array, which comprises aplurality of VC waveguides, and a plurality of Non-VC waveguides,disposed longitudinally and asymmetrically to one another, and where atleast a portion of the plural Non-VC waveguides are of different typesand/or different characteristics;

FIG. 1D is a schematic diagram of a side view of a fourth exampleembodiment of an optical fiber coupler array, configured for fan-in andfan-out connectivity and comprising a pair of optical fiber couplercomponents with a multi-core optical fiber element connected between thesecond (smaller sized) ends of the two optical fiber coupler components;

FIG. 2A is a schematic diagram of a side view of a fifth exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular first splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular firstsplice location is disposed within the single common housing structure;

FIG. 2B is a schematic diagram of a side view of a sixth exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular second splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular secondsplice location is disposed at an outer cross-sectional boundary regionof the single common housing structure;

FIG. 2C is a schematic diagram of a side view of a seventh exampleembodiment of an optical fiber coupler array, which comprises aplurality of longitudinally proximal VC waveguides at least partiallyembedded in a single common housing structure, wherein each plural VCwaveguide is spliced, at a particular third splice location, to acorresponding elongated optical device (such as an optical fiber), atleast a portion of which extends outside the single common housingstructure by a predetermined length, and wherein each particular thirdsplice location is disposed outside the single common housing structure;

FIG. 2D is a schematic diagram of a side view of an alternativeembodiment of an optical fiber coupler array, comprising a plurality oflongitudinally proximal VC waveguides at least partially embedded in asingle common housing structure, that is configured at its second end,to increase, improve, and/or optimize optical coupling to afree-space-based optical device, wherein a free-space-based device mayinclude (1) a standalone device, e.g., a lens followed by other opticalcomponents as shown in FIG. 2D, or (2) a device, which is fusionspliceable to the second coupler's end, e.g. a coreless glass element,which can serve as an end cup for power density redaction at theglass-air interface, or as a Talbot mirror for phase synchronization ofcoupler's waveguides in a Talbot cavity geometry;

FIG. 3A is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler arrays of FIGS. 1Dto 2D, above, and optionally comprising a fiducial element operable toprovide a visual identification of waveguide arrangement/characteristics(such as alignment), which may be disposed in one of several categoriesof cross-sectional regions;

FIG. 3B is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 1A,above, in which at least one VC waveguide, illustrated therein by way ofexample as a single VC waveguide, is positioned along a centrallongitudinal axis of the single common housing structure, and surroundedby a plurality of parallel proximal symmetrically positioned Non-VCwaveguides;

FIG. 3C is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which a volume of the single common housing structure mediumsurrounding the sections of all of the waveguides embedded therein,exceeds a total volume of the inner and outer cores of the section ofthe VC waveguide that is embedded within the single common housingstructure;

FIG. 3D is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which the at least one VC waveguide positioned along thecentral longitudinal axis of the single common housing structurecomprises a plurality of VC waveguides, and where in a volume of thesingle common housing structure medium surrounding the sections of allof the waveguides embedded therein, exceeds a total volume of the innerand outer cores of the sections of the plural VC waveguides that areembedded within the single common housing structure;

FIG. 3E is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3D,further comprising a central waveguide channel operable to provideoptical pumping functionality therethrough;

FIG. 3F is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3D, inwhich the VC waveguide that is positioned along the central longitudinalaxis of the single common housing structure, is of a different type,and/or comprises different characteristics from the remaining plural VCwaveguides, which, if selected to comprise enlarged inner cores, may beadvantageously utilized for increasing or optimizing optical coupling todifferent types of optical pump channels of various optical devices;

FIG. 3G is a schematic diagram of a cross-sectional view of a thirdalternative embodiment of the optical fiber coupler array of FIG. 3Babove, in which at least one VC waveguide, illustrated therein by way ofexample as a single VC waveguide, is positioned as a side-channel,off-set from the central longitudinal axis of the single common housingstructure, such that this embodiment of the optical fiber coupler arraymay be readily used as a fiber optical amplifier and or a laser, whenspliced to a double-clad optical fiber having a non-concentric core forimproved optical pumping efficiency;

FIG. 3H is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3G,above, in which the at least one VC waveguide, illustrated therein byway of example as a side-channel off-center positioned single VCwaveguide, comprises polarization maintaining properties and comprises apolarization axis that is aligned with respect to its transverseoff-center location;

FIG. 3I is a schematic diagram of a cross-sectional view of a fourthalternative embodiment of the optical fiber coupler array of FIG. 3B,above, wherein each of the centrally positioned single VC waveguide, andthe plural Non-VC waveguides, comprises polarization maintainingproperties (shown by way of example only as being induced by rod stressmembers and which may readily and alternately be induced by variousother stress or equivalent designs), and a corresponding polarizationaxis, where all of the polarization axes are aligned to one another;

FIG. 3J is a schematic diagram of a cross-sectional view of a firstalternative embodiment of the optical fiber coupler array of FIG. 3I,above, in which the polarization maintaining properties of all of thewaveguides result only from a non-circular cross-sectional shape of eachwaveguide's core (or outer core in the case of the VC waveguide), shownby way of example only as being at least in part elliptical, andoptionally comprising at least one waveguide arrangement indicationelement, positioned on an outer region of the single common housingstructure, representative of the particular cross-sectional geometricarrangement of the optical coupler array's waveguides, such that aparticular cross-sectional geometric waveguide arrangement may bereadily identified from at least one of a visual and physical inspectionof the single common coupler housing structure, the waveguidearrangement indication element being further operable to facilitatepassive alignment of a second end of the optical coupler array to atleast one optical device;

FIG. 3K is a schematic diagram of a cross-sectional view of a fifthalternative embodiment of the optical fiber coupler array of FIG. 3B,above, wherein the centrally positioned single VC waveguide, comprisespolarization maintaining properties (shown by way of example only asbeing induced by rod stress members and which may readily andalternately be induced by various other stress or equivalent designs),and a corresponding polarization axis, and optionally comprising aplurality of optional waveguide arrangement indication elements of thesame or of a different type, as described in connection with FIG. 3J;

FIG. 3L is a schematic diagram of a cross-sectional view of a secondalternative embodiment of the optical fiber coupler array of FIG. 3I,above, in which the single common housing structure comprises a crosssection having a non-circular geometric shape (shown by way of exampleas a hexagon), and in which the polarization axes of the waveguides arealigned to one another and to the single common housing structurecross-section's geometric shape, and optionally further comprises awaveguide arrangement indication element, as described in connectionwith FIG. 3J;

FIG. 4 is a schematic isometric view diagram illustrating an exampleconnection of a second end (i.e. “tip”) of the optical fiber couplerarray, in the process of connecting to plural vertical coupling elementsof an optical device in a proximal open air optical coupling alignmentconfiguration, that may be readily shifted into a butt-coupledconfiguration through full physical contact of the optical fiber couplerarray second end and the vertical coupling elements;

FIG. 5 is a schematic isometric view diagram illustrating an exampleconnection of a second end (i.e. “tip”) of the optical fiber couplerarray connected to plural edge coupling elements of an optical device ina butt-coupled configuration, that may be readily shifted into one ofseveral alternative coupling configurations, including a proximal openair optical coupling alignment configuration, and or an angled alignmentcoupling configuration;

FIG. 6 is a schematic diagram of a cross-sectional view of a previouslyknown optical fiber coupler having various drawbacks and disadvantagesreadily overcome by the various embodiments of the optical fiber couplerarray of FIGS. 1A to 5 ;

FIG. 7 is a schematic diagram, in various views, of a flexible pitchreducing optical fiber array (PROFA);

FIG. 8 is a schematic diagram of a cross-sectional view of an exampleconfiguration of the housing structure at a proximity to a first end ofthe optical coupler array. The cross-sectional view is orthogonal to thelongitudinal direction or length of the optical coupler array;

FIG. 9 is a schematic diagram of a cross-sectional view of anotherexample configuration of the housing structure at a proximity to a firstend of the optical coupler array;

FIG. 10 and FIG. 11 are schematic diagrams, in various views, ofadditional example optical coupler arrays;

FIGS. 12A, 12B, and 12C are schematic diagrams of example space divisionmultiplexers;

FIG. 13 is a schematic diagram of an example adapter with patternadaptation;

FIG. 14 is a schematic diagram of an example channel add-dropmultiplexer;

FIG. 15 is a schematic diagram of an example multiplexer with combinedpattern adaptation and channel add-drop;

FIG. 16 is a schematic diagram of an example multiplexer with a benthousing structure;

FIG. 17 is a schematic diagram of an example multiplexer with an addmultimode channel;

FIG. 18A is a schematic diagram of an example WDM-fanout device;

FIG. 18B is a schematic diagram of an example MCF-WDM device;

FIG. 19A is a schematic diagram of a cross-sectional view of an examplecombined SDM-WDM device;

FIGS. 19B, 19C, 19D, 19E, and 19F are schematic diagrams of side viewsof various examples of combined SDM-WDM devices;

FIG. 20 is a schematic diagram of a cross-sectional view of an exampleMCF-WDM device with an access region;

FIG. 21A is a schematic diagram of a cross-sectional view of an examplecombined SDM-WDM device;

FIG. 21B is a schematic diagram of an example configuration utilizingthe device shown in FIG. 21A;

FIG. 22 is a schematic diagram of another example configurationutitilizng the device shown in FIG. 21A; and

FIG. 23 is a schematic diagram of another example configurationutilizing the device shown in FIG. 21A.

DETAILED DESCRIPTION

Various implementations described herein provide improved wavelengthdivision multiplexers for space division multiplexing (SDM-WDM devices)such as wavelength division multiplexing fanout devices and pump-signalcombiners for multicore fibers (MCFs). Various implementations describedherein provide improved space division multiplexing (SDM). Somecomponents can include adapters between multicore fibers (MCFs) withdifferent core patterns. Some examples can include add-drop multiplexersfor MCFs. Some designs can include multiplexers with pattern adaptationand channel add-drop.

In some instances, improved cross sectional (or transverse) positioningof waveguides is desirable in many multichannel optical coupler arrays.In the present disclosure, some embodiments of the housing structure(e.g., a common single coupler housing structure in some cases) canallow for self-aligning waveguide arrangement at a close proximity to afirst end (e.g., hexagonal close packed arrangement in a housingstructure having circular (as shown in FIG. 8 ) or hexagonal inner crosssection) and improved (precise or near precise in some cases) crosssectional positioning of the waveguides at a second end.

Packaging of photonic integrated circuits (PICs) with low verticalprofile (perpendicular to the PIC plane) can also be desirable for avariety of applications, including optical communications and sensing.While this is easily achievable for edge couplers, surface couplers mayrequire substantial vertical length.

Accordingly, it may be advantageous to provide various embodiments of apitch reducing optical fiber array (PROFA)-based flexible optical fiberarray component that may be configured and possibly optimized tocomprise a structure that maintains all channels discretely withsufficiently low crosstalk, while providing enough flexibility toaccommodate low profile packaging. It may further be desirable toprovide a PROFA-based flexible optical fiber array component comprisinga flexible portion to provide mechanical isolation of a “PROFA-PICinterface” from the rest of the PROFA, resulting in increased stabilitywith respect to environmental fluctuations, including temperaturevariations and mechanical shock and vibration. It may be additionallydesirable to provide a PROFA-based flexible optical fiber arraycomprising multiple coupling arrays, each having multiple opticalchannels, combined together to form an optical multi-port input/output(IO) interface.

Certain embodiments are directed to an optical fiber coupler arraycapable of providing a low-loss, high-coupling coefficient interfacewith high accuracy and easy alignment between a plurality of opticalfibers (or other optical devices) with a first channel-to-channelspacing, and an optical device having a plurality of waveguideinterfaces with a second, smaller channel-to-channel spacing.Advantageously, in various embodiments, each of a larger size end and asmaller size end of the optical fiber coupler array is configurable tohave a correspondingly different (i.e., larger vs. smaller)channel-to-channel spacing, where the respective channel-to-channelspacing at each of the optical coupler array's larger and smaller endsmay be readily matched to a corresponding respective firstchannel-to-channel spacing of the plural optical fibers at the largeroptical coupler array end, and to a second channel-to-channel spacing ofthe optical device plural waveguide interfaces at the smaller opticalcoupler array end.

In various embodiments thereof, the optical coupler array includes aplurality of waveguides (at least one of which may optionally bepolarization maintaining), that comprises at least one gradually reduced“vanishing core fiber”, at least in part embedded within a commonhousing structure. Alternatively, in various additional embodimentsthereof, the coupler array may be configured for utilization with atleast one of an optical fiber amplifier and an optical fiber laser.

Each of the various embodiments of the optical coupler arrayadvantageously comprises at least one “vanishing core” (VC) fiberwaveguide, described, for example, below in connection with a VCwaveguide 30A of the optical coupler array 10A of FIG. 1A.

It should also be noted that the term “optical device” as generally usedherein, applies to virtually any single channel or multi-channel opticaldevice, or to any type of optical fiber, including, but not beinglimited to, standard/conventional optical fibers. For example, opticaldevices with which the coupler array may advantageously couple mayinclude, but are not limited to, one or more of the following:

-   -   a free-space-based optical device,    -   an optical circuit having at least one input/output edge        coupling port,    -   an optical circuit having at least one optical port comprising        vertical coupling elements,    -   a multi-mode (MM) optical fiber,    -   a double-clad optical fiber,    -   a multi-core (MC) optical fiber,    -   a large mode area (LMA) fiber,    -   a double-clad multi-core optical fiber,    -   a standard/conventional optical fiber,    -   a custom optical fiber, and/or    -   an additional optical coupler array.

In addition, while the term “fusion splice” is utilized in the variousdescriptions of the example embodiments of the coupler array providedbelow, in reference to interconnections between various optical couplerarray components, and connections between various optical coupler arraycomponents and optical device(s), it should be noted, that any otherform of waveguide or other coupler array component connectivitytechnique or methodology may be readily selected and utilized as amatter of design choice or necessity, without departing from the spiritof the invention, including but not limited to mechanical connections.

Referring now to FIG. 1A, a first example embodiment of an optical fibercoupler array is shown as an optical coupler array 10A, which comprisesa common housing structure 14A (described below), at least one VCwaveguide, shown in FIG. 1A by way of example, as a single VC waveguide30A, and at least one Non-VC waveguide, shown in FIG. 1A by way ofexample, as a pair of Non-VC waveguides 32A-1, 32A-2, each positionedsymmetrically proximally to one of the sides of the example single VCwaveguide 30A, wherein the section of the VC waveguide 30A, locatedbetween positions B and D of FIG. 1A is embedded in the common housingstructure 14A.

Before describing the coupler array 10A and its components in greaterdetail, it would be useful to provide a detailed overview of the VCwaveguide 30A, the example embodiments and alternative embodiments ofwhich, are advantageously utilized in each of the various embodiments ofthe coupler arrays of FIGS. 1A to 5 .

The VC waveguide 30A has a larger end (proximal to position B shown inFIG. 1A), and a tapered, smaller end (proximal to position C shown inFIG. 1A), and comprises an inner core 20A (comprising a material with aneffective refractive index of N-1), an outer core 22A (comprising amaterial with an effective refractive index of N-2, smaller than N-1),and a cladding 24A (comprising a material with an effective refractiveindex of N-3, smaller than N-2).

Advantageously, the outer core 22A serves as the effective cladding atthe VC waveguide 30A large end at which the VC waveguide 30A supports“M1” spatial propagating modes within the inner core 20A, where M1 islarger than 0. The indices of refraction N-1 and N-2, are preferablychosen so that the numerical aperture (NA) at the VC waveguide 30A largeend matches the NA of an optical device (e.g. an optical fiber) to whichit is connected (such as an optical device 34A-1, for example,comprising a standard/conventional optical fiber connected to the VCwaveguide 30A at a connection position 36A-1 (e.g., by a fusion splice,a mechanical connection, or by other fiber connection designs), whilethe dimensions of the inner and outer cores (20A, 22A), are preferablychosen so that the connected optical device (e.g., the optical device34A-1), has substantially the same mode field dimensions (MFD). Here andbelow we use mode field dimensions instead of commonly used mode fielddiameter (also MFD) due to the case that the cross section of the VC orNon-VC waveguides may not be circular, resulting in a non-circular modeprofile. Thus, the mode field dimensions include both the mode size andthe mode shape and equal to the mode field diameter in the case of acircularly symmetrical mode.

During fabrication of the coupler array 10A from an appropriatelyconfigured preform (comprising the VC waveguide 30A preform having thecorresponding inner and outer cores 20A, 22A, and cladding 24A), as thecoupler array 10A preform is tapered in accordance with at least onepredetermined reduction profile, the inner core 20A becomes too small tosupport all M1 modes. The number of spatial modes, supported by theinner core at the second (tapered) end is M2, where M2<M1. In the caseof a single mode waveguide, where M1=1 (corresponding to 2 polarizationmodes), M2=0, meaning that inner core is too small to support lightpropagation. The VC waveguide 30A then acts as if comprised a fiber witha single core of an effective refractive index close to N-2, surroundedby a cladding of lower index N-3.

During fabrication of the coupler array 10A, a channel-to-channelspacing S-1 at the coupler array 10A larger end (at position B, FIG.1A), decreases in value to a channel-to-channel spacing S-2 at thecoupler array 10A smaller end (at position C, FIG. 1A), in proportion toa draw ratio selected for fabrication, while the MFD value (or theinversed NA value of the VC waveguide 30A) can be either reduced,increased or preserved depending on a selected differences in refractiveindices, (N-1-N-2) and (N-2-N-3), which depends upon the desiredapplication for the optical coupler array 10A, as described below.

The capability of independently controlling the channel-to-channelspacing and the MFD values at each end of the optical coupler array is ahighly advantageous feature of certain embodiments. Additionally, thecapability to match MFD and NA values through a corresponding selectionof the sizes and shapes of inner 20A and outer 22A cores and values ofN-1, N-2, and N-3, makes it possible to utilize the optical couplerarray to couple to various waveguides without the need to use a lens.

In various embodiments thereof, the property of the VC waveguidepermitting light to continue to propagate through the waveguide corealong the length thereof when its diameter is significantly reduced,advantageously, reduces optical loss from interfacial imperfection orcontamination, and allows the use of a wide range of materials for amedium 28A of the common housing structure 14A (described below),including, but not limited to:

-   -   (a) non-optical materials (since the light is concentrated        inside the waveguide core),    -   (b) absorbing or scattering materials or materials with        refractive index larger than the refractive index of        standard/conventional fibers for reducing or increasing the        crosstalk between the channels, and    -   (c) pure-silica (e.g., the same material as is used in most        standard/conventional fiber claddings, to facilitate splicing to        multi-core, double-clad, or multi-mode fiber.

Preferably, in accordance with certain embodiments, the desired relativevalues of NA-1 and NA-2 (each at a corresponding end of the couplerarray 10A, for example, NA-1 corresponding to the coupler array 10Alarge end, and NA-2 corresponding to the coupler array 10A small end),and, optionally, the desired value of each of NA-1 and NA-2), may bedetermined by selecting the values of the refractive indices N1, N2, andN3 of the coupler array 10A, and configuring them in accordance with atleast one of the following relationships, selected based on the desiredrelative numerical aperture magnitudes at each end of the coupler array10A:

Desired NA-1/NA-2 Corresponding Relationship Relative Magnitude bet. N1,N2, N3 NA-1 (lrg. end) > NA-2 (sm. end) (N1-N2 > N2-N3) NA-1 (lrg. end)= NA-2 (sm. end) (N1-N2 = N2-N3) NA-1 (lrg. end) < NA-2 (sm. end) (N1-N2< N2-N3)

Commonly the NA of any type of fiber is determined by the followingexpression:

NA=√{square root over (n _(core) ² −n _(clad) ²)};

where n_(core) and n_(clad) are the refractive indices of fiber core andcladding respectively.

It should be noted that when the above expression is used, theconnection between the NA and the acceptance angle of the fiber is onlyan approximation. In particular, fiber manufacturers often quote “NA”for single-mode (SM) fibers based on the above expression, even thoughthe acceptance angle for a single-mode fiber is quite different andcannot be determined from the indices of refraction alone.

In accordance with certain embodiments, as used herein, the various NAvalues are preferably determined utilizing effective indices ofrefraction for both n_(core) and n_(cladding), because the effectiveindices determine the light propagation and are more meaningful in thecase of structured waveguides utilized in various embodiments. Also, atransverse refractive index profile inside a waveguide may not be flat,but rather varying around the value N1, N2, N3, or N4. In addition, thetransition between regions having refractive indices N1, N2, N3, and N4may not be as sharp as a step function due to dopant diffusion or someother intentional or non-intentional factors, and may be a smoothfunction, connecting the values of N1, N2, N3, and N4. Coupling designor optimization may involve changing both the values of N1, N2, N3, andN4 and the sizes and shapes of the regions having respective indices.

Returning now to FIG. 1A, the common coupling structure 14A, comprisesthe medium 28A, in which the section of the VC waveguide 30A locatedbetween positions B and D of FIG. 1A is embedded, and which may include,but is not limited to, at least one of the following materials:

-   -   a material, having properties prohibiting propagation of light        therethrough,    -   a material having light-absorbing optical properties,    -   a material having light scattering optical properties,    -   a material having optical properties selected such that said        fourth refractive index (N-4) is greater than said third        refractive index (N-3), and/or    -   a material having optical properties selected such that said        fourth refractive index (N-4) is substantially equal to said        third refractive index (N-3).

At the optical coupler array 10A large end (proximally to position B inFIG. 1A), the VC waveguide 30A is spliced, at a particular splicelocation 36A-1 (shown by way of example as positioned inside the commonhousing structure 14A), to a corresponding respective elongated opticaldevice 34A-1 (for example, such as an optical fiber), at least a portionof which extends outside the common housing structure 14A by apredetermined length 12A, while the Non-VC waveguides 32A-1, 32A-2 arespliced, at particular splice locations 36A-2, 36A-3, respectively(disposed outside of the common housing structure 14A), to correspondingrespective elongated optical devices 34A-2, 34A-3 (such as opticalfibers), and extending outside the common housing structure 14A by apredetermined length 12A.

Optionally, the coupler array 10A may also include a substantiallyuniform diameter tip 16A (shown between positions C and D in FIG. 1A)for coupling, at an array interface 18A with the interface 42A of anoptical waveguide device 40A. The uniform diameter tip 16A may be usefulin certain interface applications, such as for example shown in FIGS.1D, 4 and 5 . Alternatively, the coupler array 10A may be fabricatedwithout the tip 16A (or have the tip 16A removed after fabrication),such that coupling with the optical device interface 42A, occurs at acoupler array 10A interface at position C of FIG. 1A.

In an alternative embodiment, if the optical device 40A comprises adouble-clad fiber, when the small end of the coupler array 10A iscoupled (for example, fusion spliced) to the optical device interface42A, at least a portion of the common housing structure 14A proximal tothe splice position (such as at least a portion of the tip 16A), may becoated with a low index medium (not shown), extending over the spliceposition and up to the double-clad fiber optical device 40A outercladding (and optionally extending over a portion of the double-cladfiber optical device 40A outer cladding that is proximal to the spliceposition).

Referring now to FIG. 1B, a second example embodiment of the opticalfiber coupler array, is shown as a coupler array 10B. The coupler array10B comprises a common housing structure 14B, at least one VC waveguide,shown in FIG. 1B by way of example, as a single VC waveguide 30B, and atleast one Non-VC waveguide, shown in FIG. 1B by way of example, as asingle Non-VC waveguide 32B, disposed in parallel proximity to the VCwaveguide 30B, where a portion of the optical coupler array 10B, hasbeen configured to comprise a larger channel-to-channel spacing valueS2′ at its small end, than the corresponding channel-to-channel spacingvalue S2 at the small end of the optical coupler array 10A, of FIG. 1A.This configuration may be readily implemented by transversely cuttingthe optical fiber array 10A at a position C′, thus producing the commonhousing structure 14B that is shorter than the common housing structure14A and resulting in a new, larger diameter array interface 18B, havingthe larger channel-to-channel spacing value S2′.

Referring now to FIG. 1C, a third example embodiment of the opticalfiber coupler array, is shown as a coupler array 10C. The coupler array10C comprises a plurality of VC waveguides, shown in FIG. 1C as VCwaveguides 30C-1, and 30C-2, and a plurality of Non-VC waveguides, shownin FIG. 1C as Non-VC waveguides 32C-1, 32C-2, and 32C-a, all disposedlongitudinally and asymmetrically to one another, wherein at least aportion of the plural Non-VC waveguides are of different types and/ordifferent characteristics (such as single mode or multimode orpolarization maintaining etc.)—for example, Non-VC waveguides 32C-1,32C-2 are of a different type, or comprise different characteristicsfrom the Non-VC waveguide 32C-a. Additionally, any of the VC or Non-VCwaveguides (such as, for example, the Non-VC waveguide 32C-a) canreadily extend beyond the coupler array 10C common housing structure byany desired length, and need to be spliced to an optical deviceproximally thereto.

Referring now to FIG. 1D, a fourth example embodiment of the opticalfiber coupler array that is configured for multi-core fan-in and fan-outconnectivity, and shown as a coupler array 50. The coupler array 50comprises a pair of optical fiber coupler array components (10D-1 and10D-2), with a multi-core optical fiber element 52 connected (e.g., byfusion splicing at positions 54-1 and 54-2) between the second (smallersized) ends of the two optical fiber coupler array components (10D-1,10D-2). Preferably, at least one of the VC waveguides in each of thecoupler array components (10D-1, 10D-2) is configured to increase ormaximize optical coupling to a corresponding selected core of themulti-core optical fiber element 52, while decreasing or minimizingoptical coupling to all other cores thereof.

Referring now to FIG. 2A, a fifth example embodiment of the opticalfiber coupler array, is shown as a coupler array 100A. The coupler array100A comprises a plurality of longitudinally proximal VC waveguides atleast partially embedded in a single common housing structure 104A,shown by way of example only, as plural VC waveguides 130A-1, 130A-2.Each plural VC waveguide 130A-1, 130A-2 is spliced, at a particularsplice location 132A-1, 132A-2, respectively, to a correspondingrespective elongated optical device 134A-1, 134A-2 (such as an opticalfiber), at least a portion of which extends outside the common housingstructure 104A by a predetermined length 102A, and wherein eachparticular splice location 132A-1, 132A-2 is disposed within the commonhousing structure 104A.

Referring now to FIG. 2B, a sixth example embodiment of the opticalfiber coupler array, is shown as a coupler array 100B.

The coupler array 100B comprises a plurality of longitudinally proximalVC waveguides at least partially embedded in a single common housingstructure 104B, shown by way of example only, as plural VC waveguides130B-1, 130B-2. Each plural VC waveguide 130B-1, 130B-2 is spliced, at aparticular splice location 132B-1, 132B-2, respectively, to acorresponding respective elongated optical device 134B-1, 134B-2 (suchas an optical fiber), at least a portion of which extends outside thecommon housing structure 104B by a predetermined length 102B, andwherein each particular splice location 132B-1, 132B-2 is disposed at anouter cross-sectional boundary region of the common housing structure104B.

Referring now to FIG. 2C, a seventh example embodiment of the opticalfiber coupler array, is shown as a coupler array 100C.

The coupler array 100C comprises a plurality of longitudinally proximalVC waveguides at least partially embedded in a single common housingstructure 104C, shown by way of example only, as plural VC waveguides130C-1, 130C-2. Each plural VC waveguide 130C-1, 130C-2 is spliced, at aparticular splice location 132C-1, 132C-2, respectively, to acorresponding respective elongated optical device 134C-1, 134C-2 (suchas an optical fiber), at least a portion of which extends outside thecommon housing structure 104C by a predetermined length 102C, andwherein each particular splice location 132C-1, 132C-2 is disposedoutside of the common housing structure 104C.

Referring now to FIG. 2D, an alternative embodiment of the optical fibercoupler array, is shown as a coupler array 150. The coupler array 150comprises a plurality of longitudinally proximal VC waveguides at leastpartially embedded in a single common housing structure, that isconfigured at its second end, to increase or optimize optical couplingto a free-space-based optical device 152. The free-space-based opticaldevice 152 may comprise a lens 154 followed by an additional opticaldevice component 156, which may comprise, by way of example, a MEMSmirror or volume Bragg grating. The combination of the coupler and thefree-space-based optical device 152 may be used as an optical switch orWDM device for spectral combining or splitting of light signals 160 b(representative of the light coupler array 150 output light signals 160a after they have passed through the lens 154.) In this case, one of thefibers may be used as an input and all others for an output or viceversa. In another embodiment, a free-space-based device 152 can befusion spliceable to the second coupler's end. This device may be acoreless glass element, which can serve as an end cup for power densityredaction at the glass-air interface. In another modification, thecoreless element can serve as a Talbot mirror for phase synchronizationof coupler's waveguides in a Talbot cavity geometry

Prior to describing the various embodiments shown in FIGS. 3A to 3L ingreater detail, it should be understood that whenever a “plurality” or“at least one” coupler component/element is indicated below, thespecific quantity of such coupler components/elements that may beprovided in the corresponding embodiment of the coupler array, may beselected as a matter of necessity, or design choice (for example, basedon the intended industrial application of the coupler array), withoutdeparting from the spirit of the present invention. Accordingly, in thevarious FIGS. 3A to 3L, single or individual coupler arraycomponents/elements are identified by a single reference number, whileeach plurality of the coupler component/elements is identified by areference number followed by a “(1 . . . n)” designation, with “n” beinga desired number of plural coupler elements/components (and which mayhave a different value in any particular coupler array embodimentdescribed below).

Also, all the waveguides VC and Non-VC are shown with a circularcross-section of the inner and outer core and cladding only by example.Other shapes of the cross-sections of the inner and outer core andcladding (for example, hexagonal, rectangular or squared) may beutilized without departure from the current invention. The specificchoice of shape is based on various requirements, such as channel shapeof the optical device, channel positional geometry (for example,hexagonal, rectangular or square lattice), or axial polarizationalignment mode.

Similarly, unless otherwise indicated below, as long as variousrelationships set forth below (for example, the relative volumerelationship set forth below with respect to optical coupler arrays 200Cand 200D of FIGS. 3C and 3D, respectively, and the feature, set forthbelow in connection with the coupler array 200H of FIG. 3H, that the PMVC waveguide 204H is positioned longitudinally off-centered transverselyfrom the coupler array 200H central longitudinal axis), are adhered to,the sizes, relative sizes, relative positions and choices of compositionmaterials, are not limited to the example sizes, relative sizes,relative positions and choices of composition materials, indicated belowin connection with the detailed descriptions of the coupler arrayembodiments of FIGS. 3A to 3L, but rather they may be selected by oneskilled in the art as a matter of convenience or design choice, withoutdeparting from the spirit of the present invention.

Finally, it should be noted that each of the various single commonhousing structure components 202A to 202L, of the various coupler arrays200A to 200L of FIGS. 3A to 3L, respectively, may be composed of amedium having the refractive index N-4 value in accordance with anapplicable one of the above-described relationships with the values ofother coupler array component refractive indices N-1, N-2, and N-3, andhaving properties and characteristics selected from the variouscontemplated example medium composition parameters described above inconnection with medium 28A of FIG. 1A.

Referring now to FIG. 3A, a first alternative embodiment of the opticalfiber coupler array embodiments of FIGS. 1D to 2D, is shown as a couplerarray 200A in which all waveguides are VC waveguides. The coupler array200A comprises a single common housing 202A, and plurality of VCwaveguides 204A-(1 . . . n), with n being equal to 19 by way of exampleonly, disposed centrally along the central longitudinal axis of thehousing 202A. The coupler array 200A may also comprise an optional atleast one fiducial element 210A, operable to provide one or more usefulproperties to the coupler array, including, but not limited to:

-   -   enabling visual identification (at at least one of the coupler        array's ends) of the coupler array waveguide arrangement; and    -   facilitating passive alignment of at least one of the coupler        array ends to at least one optical device.

Furthermore, when deployed in optical coupler array embodiments thatcomprise at least one polarization maintaining VC waveguide (such as theoptical coupler array embodiments described below in connection withFIGS. 3H-3L), a fiducial element is further operable to:

-   -   enable visual identification of the optical coupler array's        particular polarization axes alignment mode (such as described        below in connection with FIGS. 3H-3L); and    -   serve as a geometrically positioned reference point for        alignment thereto, of one or more polarization axis of PM        waveguides in a particular optical coupler array.

The fiducial element 210A may comprise any of the various types offiducial elements known in the art, selected as a matter of designchoice or convenience without departing from the spirit of theinvention—for example, it may be a dedicated elongated elementpositioned longitudinally within the common housing structure 202A inone of various cross-sectional positions (such as positions X or Y,shown in FIG. 3A. Alternatively, the fiducial element 210A may comprisea dedicated channel not used for non-fiducial purposes, for example,replacing one of the waveguides 204A-(1 . . . n), shown by way ofexample only at position Z in FIG. 3A.

Referring now to FIG. 3B, a first alternative embodiment of the opticalfiber coupler array 10A of FIG. 1A, above, is shown as a coupler array200B, that comprises a single housing structure 202B, and at least oneVC waveguide, shown in FIG. 3B by way of example as a VC waveguide 204B,and a plurality of Non-VC waveguides 206B-(1 . . . n), with n beingequal to 18 by way of example only. The VC waveguide 204B is positionedalong a central longitudinal axis of the common housing structure 202B,and circumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206B-(1 . . . n).

Referring now to FIG. 3C, a first alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200C that comprises a single housing structure 202C, a VC waveguide204C, and a plurality of Non-VC waveguides 206C-(1 . . . n), with nbeing equal to 18 by way of example only. The VC waveguide 204C ispositioned along a central longitudinal axis of the common housingstructure 202C, and circumferentially and symmetrically surrounded byproximal parallel plural Non-VC waveguides 206C-(1 . . . n). The couplerarray 200C is configured such that a volume of the common housingstructure 202C medium, surrounding the sections of all of the waveguidesembedded therein (i.e., the VC waveguide 204C and the plural Non-VCwaveguides 206C-(1 . . . n)), exceeds a total volume of the inner andouter cores of the section of the VC waveguide 204C that is embeddedwithin the single common housing structure 202C.

Referring now to FIG. 3D, a first alternative embodiment of the opticalfiber coupler array 200C of FIG. 3C, above, is shown as a coupler array200D that comprises a single housing structure 202D, a plurality of VCwaveguides 204D-(1 . . . N), with N being equal to 7 by way of exampleonly, and a plurality of Non-VC waveguides 206D-(1 . . . n), with nbeing equal to 12 by way of example only. The plural VC waveguides204D-(1 . . . N) are positioned along a central longitudinal axis of thecommon housing structure 202D, and circumferentially and symmetricallysurrounded by proximal parallel plural Non-VC waveguides 206D-(1 . . .n). The coupler array 200D is configured such that a volume of thecommon housing structure 202D medium, surrounding the sections of all ofthe waveguides embedded therein (e.g., the plural VC waveguides 204D-(1. . . N), and the plural Non-VC waveguides 206D-(1 . . . n)), exceeds atotal volume of the inner and outer cores of the section of the pluralVC waveguides 204D-(1 . . . N) that are embedded within the singlecommon housing structure 202D.

Referring now to FIG. 3E, a first alternative embodiment of the opticalfiber coupler array 200D of FIG. 3D, above, is shown as a coupler array200E, that comprises a single housing structure 202E, a plurality of VCwaveguides 204E-(1 . . . N), with N being equal to 6 by way of exampleonly, a plurality of Non-VC waveguides 206E-(1 . . . n), with n beingequal to 12 by way of example only, and a separate single Non-VCwaveguide 206E′. The Non-VC waveguide 206E′, is preferably operable toprovide optical pumping functionality therethrough, and is positionedalong a central longitudinal axis of the common housing structure 202Eand circumferentially and symmetrically surrounded by proximal parallelplural VC waveguides 204E-(1 . . . N), that are in turncircumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206E-(1 . . . n).

Referring now to FIG. 3F, a second alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200F, that comprises a single housing structure 202F, a plurality of VCwaveguides 204F-(1 . . . N), with N being equal to 6 by way of exampleonly, a separate single VC waveguide 204F′, and a plurality of Non-VCwaveguides 206F-(1 . . . n), with n being equal to 12 by way of exampleonly, that preferably each comprise enlarged inner cores of sufficientdiameter to increase or optimize optical coupling to different types ofoptical pump channels of various optical devices, to which the couplerarray 200F may be advantageously coupled. The VC waveguide 204F′, ispositioned along a central longitudinal axis of the common housingstructure 202F, and circumferentially and symmetrically surrounded byproximal parallel plural VC waveguides 204F-(1 . . . N), that are inturn circumferentially and symmetrically surrounded by proximal parallelplural Non-VC waveguides 206F-(1 . . . n).

Referring now to FIG. 3G, a third alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200G, that comprises a single housing structure 202G, and at least oneVC waveguide, shown in FIG. 3G by way of example as a VC waveguide 204G,and a plurality of Non-VC waveguides 206G-(1 . . . n), with n beingequal to 18 by way of example only. The VC waveguide 204G is positionedas a side-channel, off-set from the central longitudinal axis of thesingle common housing structure 202G, such that optical fiber couplerarray 200G may be readily used as a fiber optical amplifier and or alaser, when spliced to a double-clad optical fiber (not shown) having anon-concentric core for improved optical pumping efficiency. It shouldbe noted that because a double-clad fiber is a fiber in which both thecore and the inner cladding have light guiding properties, most opticalfiber types, such as SM, MM, LMA, or MC (multi-core), whetherpolarization maintaining or not, and even standard (e.g., conventional)single mode optical fibers, can be converted into a double-clad fiber bycoating (or recoating) the fiber with a low index medium (forming theouter cladding).

Optionally, when the second end of the coupler array 200G is spliced toa double-clad fiber (not shown), at least a portion of the commonhousing structure 202G proximal to the splice point with the double-cladfiber (not-shown), may be coated with a low index medium extending overthe splice point and up to the double-clad fiber's outer cladding (andoptionally extending over a portion of the outer cladding that isproximal to the splice point).

Referring now to FIGS. 3H to 3L, in various alternative exampleembodiments of the optical coupler, at least one of the VC waveguidesutilized therein, and, in certain embodiments, optionally at least oneof the Non-VC waveguides, may comprise a polarization maintaining (PM)property. By way of example, the PM property of a VC waveguide mayresult from a pair of longitudinal stress rods disposed within the VCwaveguide outside of its inner core and either inside, or outside, ofthe outer core (or through other stress elements), or the PM propertymay result from a noncircular inner or outer core shape, or from otherPM-inducing optical fiber configurations (such as in bow-tie orelliptically clad PM fibers). In various embodiments of the opticalfiber in which at least one PM waveguide (VC and/or Non-VC) is utilized,an axial alignment of the PM waveguides (or waveguide), in accordancewith a particular polarization axes alignment mode may be involved.

In accordance with certain embodiments, a polarization axes alignmentmode may comprise, but is not limited to, at least one of the following:

-   -   axial alignment of a PM waveguide's polarization axis to the        polarization axes of other PM waveguides in the optical coupler;        when a PM waveguide is positioned off-center: axial alignment of        a PM waveguide's polarization axis to its transverse        cross-sectional (geometric) position within the optical coupler;    -   when the single common housing structure of the optical coupler        comprises a non-circular geometric shape (such as shown by way        of example in FIG. 3L): axial alignment of a PM waveguide's        polarization axis to a geometric feature of the common housing        structure outer shape;    -   in optical coupler embodiments comprising one or more waveguide        arrangement indicators, described below, in connection with        FIGS. 3J-3L: axial alignment of a PM waveguide's polarization        axis to at least one geometric characteristic thereof;    -   in optical coupler embodiments comprising at least one fiducial        element 210A, as described above in connection with FIG. 3A:        axial alignment of a PM waveguide's polarization axis to a        geometric position of the at least one fiducial element 210A;

The selection of a specific type of polarization axes alignment mode forthe various embodiments of the optical coupler is preferably governed byat least one axes alignment criterion, which may include, but which isnot limited to: alignment of PM waveguides' polarization axes in ageometric arrangement that increases or maximizes PM properties thereof;and/or satisfying at least one requirement of one or more intendedindustrial application for the coupler array.

Referring now to FIG. 3H, a first alternative embodiment of the opticalfiber coupler array 200G of FIG. 3G, above, is shown as a coupler array200H, that comprises a single housing structure 202H, and at least oneVC waveguide, shown in FIG. 3H by way of example as a PM VC waveguide204H having polarization maintaining properties, and a plurality ofNon-VC waveguides 206H-(1 . . . n), with n being equal to 18 by way ofexample only. The PM VC waveguide 204H is positioned as a side-channel,off-set from the central longitudinal axis of the single common housingstructure 202H, and comprises a polarization axis that is aligned, byway of example, with respect to the transverse off-center location ofthe PM VC waveguide 204H.

Referring now to FIG. 3I, a fourth alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200I, that comprises a single housing structure 202I, and at least oneVC waveguide, shown in FIG. 3I by way of example as a PM VC waveguide204I having polarization maintaining properties, and a plurality of PMNon-VC waveguides 206I-(1 . . . n), with n being equal to 18 by way ofexample only, each also having polarization maintaining properties. ThePM VC waveguide 204I is positioned along a central longitudinal axis ofthe common housing structure 202I, and circumferentially andsymmetrically surrounded by proximal parallel plural PM Non-VCwaveguides 206I-(1 . . . n). By way of example, the coupler array 200Icomprises a polarization axes alignment mode in which the polarizationaxes of each of the PM VC waveguide 204I and of the plural PM Non-VCwaveguides 206I-(1 . . . n) are aligned to one another. The PMproperties of the PM VC waveguide 204I and of the plural PM Non-VCwaveguides 206I-(1 . . . n) are shown, by way of example only, as beinginduced by rod stress members (and which may readily and alternately beinduced by various other stress, or equivalent designs)).

Referring now to FIG. 3J, a first alternative embodiment of the opticalfiber coupler array 200I of FIG. 3I, above, is shown as a coupler array200J, that comprises a single housing structure 202J, and at least oneVC waveguide, shown in FIG. 3J by way of example as a PM VC waveguide204J having polarization maintaining properties, and a plurality of PMNon-VC waveguides 206J-(1 . . . n), with n being equal to 18 by way ofexample only, each also having polarization maintaining properties. ThePM VC waveguide 204J is positioned along a central longitudinal axis ofthe common housing structure 202J, and circumferentially andsymmetrically surrounded by proximal parallel plural PM Non-VCwaveguides 206J-(1 . . . n). The PM properties of the PM VC waveguide204J and of the plural PM Non-VC waveguides 206J-(1 . . . n) are shown,by way of example only, as resulting only from a non-circularcross-sectional shape (shown by way of example only as being at least inpart elliptical), of each plural PM Non-VC waveguide 206J-(1 . . . n)core (and from a non-circular cross-sectional shape of the outer core ofthe PM VC waveguide 204J).

The coupler array 200J optionally comprises at least one waveguidearrangement indication element 208J, positioned on an outer region ofthe common housing structure 202J, that is representative of theparticular cross-sectional geometric arrangement of the optical couplerarray 200J waveguides (i.e., of the PM VC waveguide 204J and of theplural PM Non-VC waveguides 206J-(1 . . . n)), such that a particularcross-sectional geometric waveguide arrangement may be readilyidentified from at least one of a visual and physical inspection of thecommon coupler housing structure 202J that is sufficient to examine thewaveguide arrangement indication element 208J. Preferably, the waveguidearrangement indication element 208J may be configured to be furtheroperable to facilitate passive alignment of a second end of the opticalcoupler array 200J to at least one optical device (not shown).

The waveguide arrangement indication element 208J, may comprise, but isnot limited to, one or more of the following, applied to the commonhousing structure 202J outer surface: a color marking, and/or a physicalindicia (such as an groove or other modification of the common housingstructure 202J outer surface, or an element or other member positionedthereon). Alternatively, the waveguide arrangement indication element208J may actually comprise a specific modification to, or definition of,the cross-sectional geometric shape of the common housing structure 202J(for example, such as a hexagonal shape of a common housing structure202L of FIG. 3L, below, or another geometric shape).

By way of example, the coupler array 200J may comprise a polarizationaxes alignment mode in which the polarization axes of each of the PM VCwaveguide 204J and of the plural PM Non-VC waveguides 206J-(1 . . . n)are aligned to one another, or to the waveguide arrangement indicationelement 208J.

Referring now to FIG. 3K, a fifth alternative embodiment of the opticalfiber coupler array 200B of FIG. 3B, above, is shown as a coupler array200K, that comprises a single housing structure 202K, and at least oneVC waveguide, shown in FIG. 3K by way of example as a PM VC waveguide204K having polarization maintaining properties, and a plurality ofNon-VC waveguides 206K-(1 . . . n), with n being equal to 18 by way ofexample only. The PM VC waveguide 204K is positioned along a centrallongitudinal axis of the common housing structure 202K, andcircumferentially and symmetrically surrounded by proximal parallelplural PM Non-VC waveguides 206K-(1 . . . n). The PM properties of thePM VC waveguide 204K are shown, by way of example only, as being inducedby rod stress members (and which may readily and alternately be inducedby various other stress, or equivalent approaches)). The coupler array200K, may optionally comprise a plurality of waveguide arrangementindication elements—shown by way of example only, as waveguidearrangement indication elements 208K-a and 208K-b, which may each be ofthe same, or of a different type, as described above, in connection withthe waveguide arrangement indication element 208J of FIG. 3J.

Referring now to FIG. 3L, a second alternative embodiment of the opticalfiber coupler array 200I of FIG. 3I, above, is shown as a coupler array200L, that comprises a single housing structure 202L comprising a crosssection having a non-circular geometric shape (shown by way of exampleas a hexagon), and at least one VC waveguide, shown in FIG. 3L by way ofexample as a PM VC waveguide 204L having polarization maintainingproperties, and a plurality of PM Non-VC waveguides 206L-(1 . . . n),with n being equal to 18 by way of example only, each also havingpolarization maintaining properties. The PM VC waveguide 204L ispositioned along a central longitudinal axis of the common housingstructure 202L, and circumferentially and symmetrically surrounded byproximal parallel plural PM Non-VC waveguides 206L-(1 . . . n).

By way of example, the coupler array 200L comprises a polarization axesalignment mode in which the polarization axes of each of the PM VCwaveguide 204L and of the plural PM Non-VC waveguides 206L-(1 . . . n)are aligned to one another, and to the common housing structure 202Lcross-sectional geometric shape. The PM properties of the PM VCwaveguide 204L and of the plural PM Non-VC waveguides 206L-(1 . . . n)are shown, by way of example only, as being induced by rod stressmembers (and which may readily and alternately be induced by variousother stress, or equivalent designs)). The coupler array 200K, mayoptionally comprise a waveguide arrangement indication element 208L-awhich may comprise any of the configurations described above, inconnection with the waveguide arrangement indication element 208J ofFIG. 3J.

Referring now to FIG. 4 , a second end 302 (i.e. “tip”) of the opticalfiber coupler array is shown, by way of example, as being in the processof connecting to plural vertical coupling elements 306 of an opticaldevice 304 in a proximal open air optical coupling alignmentconfiguration, that may be readily shifted into a butt-coupledconfiguration through full physical contact of the optical fiber couplerarray second end 302 and the vertical coupling elements 306.

Referring now to FIG. 5 a second end 322 (i.e. “tip”) of the opticalfiber coupler array is shown, by way of example, as being in the processof connecting to plural edge coupling elements 326 of an optical device324 in a butt-coupled configuration, that may be readily shifted intoone of several alternative coupling configuration, including a proximalopen air optical coupling alignment configuration, and or an angledalignment coupling configuration.

In at least one alternative embodiment, the optical coupler array (i.e.,such as optical coupler arrays 200D to 200L of FIGS. 3C to 3L) may bereadily configured to pump optical fiber lasers, and/or optical fiberamplifiers (or equivalent devices). In a preferred embodiment thereof, apumping-enabled coupler array comprises a central channel (i.e.,waveguide), configured to transmit a signal (i.e., serving as a “signalchannel”) which will thereafter be amplified or utilized to generatelasing, and further comprises at least one additional channel (i.e.,waveguide), configured to provide optical pumping functionality (i.e.,each serving as a “pump channel”). In various example alternativeembodiments thereof, the pumping-enabled coupler array may comprise thefollowing in any desired combination thereof:

-   -   at least one of the following signal channels: a single mode        signal channel configured for increased or optimum coupling to a        single mode amplifying fiber at at least one predetermined        signal or lasing wavelength, a multimode signal channel        configured for increased or optimum coupling to a multimode        amplifying fiber at at least one predetermined signal or lasing        wavelength, and    -   at least one of the following pumping channels: a single mode        pumping channel configured for increased or optimum coupling to        a single mode pump source at at least one predetermined pumping        wavelength, a multimode pumping channel configured for increased        or optimum coupling to a multimode pump source at at least one        predetermined pumping wavelength.

Optionally, to increase or maximize pumping efficiency, thepumping-enabled coupler array may be configured to selectively utilizeless than all the available pumping channels. It should also be notedthat, as a matter of design choice, and without departing from thespirit of the invention, the pumping-enabled coupler array may beconfigured to comprise:

-   -   a. At least one signal channel, each disposed in a predetermined        desired position in the coupler array structure;    -   b. At least one pumping channel, each disposed in a        predetermined desired position in the coupler array structure;        and    -   c. Optionally—at least one additional waveguide for at least one        additional purpose other than signal transmission or pumping        (e.g., such as a fiducial marker for alignment, for fault        detection, for data transmission, etc.)

Advantageously, the pump channels could be positioned in any transverseposition within the coupler, including along the central longitudinalaxis. The pump channels may also comprise, but are not limited to, atleast one of any of the following optical fiber types: SM, MM, LMA, orVC waveguides. Optionally, any of the optical fiber(s) being utilized asan optical pump channel (regardless of the fiber type) in the couplermay comprise polarization maintaining properties.

In yet another example embodiment, the pumping-enabled coupler array maybe configured to be optimized for coupling to a double-clad fiber—inthis case, the signal channel of the coupler array would be configuredor optimized for coupling to the signal channel of the double-cladfiber, while each of the at least one pumping channels would beconfigured or optimized to couple to the inner cladding of thedouble-clad fiber.

In essence, the optical coupler arrays, shown by way of example invarious embodiments, may also be readily implemented as high density,multi-channel, optical input/output (I/O) for fiber-to-chip andfiber-to-optical waveguides. The optical fiber couplers may readilycomprise at least the following features:

-   -   Dramatically reduced channel spacing and device footprint (as        compared to previously known solutions)    -   Scalable channel count    -   All-glass optical path    -   Readily butt-coupled or spliced at their high density face        without the need of a lens, air gap, or a beam spreading medium    -   May be fabricated through a semi-automated production process    -   Broad range of customizable parameters: wavelength, mode field        size, channel spacing, array configuration, fiber type.

The optical fiber couplers may be advantageously utilized for at leastthe following applications, as a matter of design choice or convenience,without departing from the spirit of the invention:

-   -   Coupling to waveguides:        -   PIC or PCB-based (single-mode or multimode)        -   Multicore fibers        -   Chip edge (1D) or chip face (2D) coupling        -   NA optimized for the application, factoring in:            -   Packaging alignment needs            -   Chip processing needs/waveguide up-tapering        -   Polarization maintaining properties may be readily            configured    -   Coupling to chip-based devices: e.g. VCSELs, photodiodes,        vertically coupled gratings    -   Laser diode coupling    -   High density equipment Input/Output (I/O)

Accordingly, when implemented, the various example embodiments of theoptical fiber couplers comprise at least the following advantages, ascompared to currently available competitive solutions:

-   -   Unprecedented density    -   Low-loss coupling (<0.5 dB)    -   Operational stability    -   Form factor support    -   Broad spectral range    -   Matching NA    -   Scalable channel count    -   Polarization maintenance

Referring now to FIG. 7 , at least one example embodiment of a flexibleoptical coupler array is shown as a flexible pitch reducing opticalfiber array (PROFA) coupler 450. Although various features of theexample PROFA coupler may be described with respect to FIG. 7 , anyfeature described above can be implemented in any combination with aflexible PROFA coupler. For example, any of the features described withrespect to FIGS. 1A-5 may be utilized in a flexible PROFA coupler.Further, any feature described with respect to FIGS. 1A-5 may becombined with any feature described with respect to FIG. 7 .

With continued reference to FIG. 7 , the example flexible PROFA coupler450 shown in FIG. 7 can be configured for use in applications whereinterconnections with low crosstalk and sufficient flexibility toaccommodate low profile packaging are desired. The vanishing coreapproach, described herein and in U.S. Patent Application PublicationNo. 2013/0216184, entitled “CONFIGURABLE PITCH REDUCING OPTICAL FIBERARRAY”, which is hereby incorporated herein in its entirety, allows forthe creation of a pitch reducing optical fiber array (PROFA)coupler/interconnect operable to optically couple, for example, aplurality of optical fibers to an optical device (e.g., a PIC), whichcan be butt-coupled to an array of vertical grating couplers (VGCs). Ifthe cross sectional structure of the coupler 450 has an additional layerof refractive index, N-2A, even lower than N2, as described herein andin U.S. Patent Application Publication No. 2013/0216184, the vanishingcore approach can be utilized once more to reduce the outside diameterfurther without substantially compromising the channel crosstalk. Thisfurther reduction can advantageously provide certain embodiments with aflexible region which has a reduced cross section between a first andsecond end.

In some preferred embodiments, the difference (N-2A minus N-3) is largerthan the differences (N-2 minus N-2A) or (N-1 minus N-2), resulting in ahigh NA, bend insensitive waveguide, when the light is guided by theadditional layer having refractive index N-2A. Also, in some preferredembodiments, after the outside diameter of the coupler 450 is reducedalong a longitudinal length from one end to form the flexible region,the outer diameter can then be expanded along the longitudinal lengthtoward the second end, resulting in a lower NA waveguide with largercoupling surface area at the second end.

For example, as illustrated in FIG. 7 , certain embodiments of anoptical coupler array 450 can comprise an elongated optical element 1000having a first end 1010, a second end 1020, and a flexible portion 1050therebetween. The optical element 1000 can include a coupler housingstructure 1060 and a plurality of longitudinal waveguides 1100 embeddedin the housing structure 1060. The waveguides 1100 can be arranged withrespect to one another in a cross-sectional geometric waveguidearrangement. In FIG. 7 , the example cross-sectional geometric waveguidearrangements of the waveguides 1100 for the first end 1010, the secondend 1020, and at a location within the flexible portion 1050 are shown.The cross-sectional geometric waveguide arrangement of the waveguides1100 for an intermediate location 1040 between the first end 1010 andthe flexible portion 1050 is also shown. As illustrated by the shadedregions within the cross sections and as will be described herein, lightcan be guided through the optical element 1000 from the first end 1010to the second end 1020 through the flexible portion 1050. As also shownin FIG. 7 , this can result in a structure, which maintains all channelsdiscretely with sufficiently low crosstalk, while providing enoughflexibility (e.g., with the flexible portion 1050) to accommodate lowprofile packaging.

The level of crosstalk and/or flexibility can depend on the applicationof the array. For example, in some embodiments, a low crosstalk can beconsidered within a range from −45 dB to −35 dB, while in otherembodiments, a low crosstalk can be considered within a range from −15dB to −5 dB. Accordingly, the level of crosstalk is not particularlylimited. In some embodiments, the crosstalk can be less than or equal to−55 dB, −50 dB, −45 dB, −40 dB, −35 dB, −30 dB, −25 dB, −20 dB, −15 dB,−10 dB, 0 dB, or any values therebetween (e.g., less than or equal to−37 dB, −27 dB, −17 dB, −5 dB, etc.) In some embodiments, the crosstalkcan be within a range from −50 dB to −40 dB, from −40 dB to −30 dB, from−30 dB to −20 dB, from −20 dB to −10 dB, from −10 dB to 0 dB, from −45dB to −35 dB, from −35 dB to −25 dB, from −25 dB to −15 dB, from −15 dBto −5 dB, from −10 dB to 0 dB, any combinations of these ranges, or anyranges formed from any values from −55 dB to 0 dB (e.g., from −52 dB to−37 dB, from −48 dB to −32 dB, etc.).

The flexibility can also depend on the application of the array. Forexample, in some embodiments, good flexibility of the flexible portion1050 can comprise bending of at least 90 degrees, while in otherembodiments, a bending of at least 50 degrees may be acceptable.Accordingly, the flexibility is not particularly limited. In someembodiments, the flexibility can be at least 45 degrees, 50 degrees, 55degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90degrees, 100 degrees, 110 degrees, 120 degrees, or at least any valuetherebetween. In some embodiments, the flexible portion 1050 can bend ina range formed by any of these values, e.g., from 45 to 55 degrees, from50 to 60 degrees, from 60 to 70 degrees, from 70 to 80 degrees, from 80to 90 degrees, from 90 to 100 degrees, from 100 to 110 degrees, from 110to 120 degrees, or any combinations of these ranges, or any rangesformed by any values within these ranges (e.g., from 50 to 65 degrees,from 50 to 85 degrees, from 65 to 90 degrees, etc.) In otherembodiments, the flexible portion 1050 can bend more or less than thesevalues. Bending can typically be associated with light scattering.However, various embodiments can be configured to bend as describedherein (e.g., in one of the ranges described above) and achieverelatively low crosstalk as described herein (e.g., in one of the rangesdescribed above).

In various applications, the flexible portion 1050 might not bend inuse, however the flexibility can be desired for decoupling the first1010 or second 1020 end from other parts of the coupler array 450. Forexample, the flexible portion 1050 of the flexible PROFA coupler 450 canprovide mechanical isolation of the first end 1010 (e.g., a PROFA-PICinterface) from the rest of the PROFA, which results in increasedstability with respect to environmental fluctuations, includingtemperature variations and mechanical shock and vibration.

In the example shown in FIG. 7 , the coupler array 450 can be operableto optically couple with a plurality of optical fibers 2000 and/or withan optical device 3000. The optical fibers 2000 and optical device 3000can include any of those described herein. The coupler array 450 cancouple with the optical fibers 2000 via the plurality of waveguides 1100at the first end 1010. In addition, the coupler array 450 can couplewith the optical device 3000 via the plurality of waveguides 1100 at thesecond end 1020. As described herein, the plurality of waveguides 1100can include at least one VC waveguide 1101. FIG. 7 illustrates all ofthe waveguides 1100 as VC waveguides. However, one or more Non-VCwaveguides may also be used. In addition, FIG. 7 illustrates 7 VCwaveguides, yet any number of VC and/or Non-VC waveguides can be used.

As also shown in the cross sections, each of the waveguides 1100 can bedisposed at an individual corresponding cross-sectional geometricposition, relative to other waveguides of the plurality of waveguides1100. Although FIG. 7 shows a waveguide surrounded by 6 otherwaveguides, the cross-sectional geometric waveguide arrangement is notlimited and can include any arrangement known in the art or yet to bedeveloped including any of those shown in FIGS. 3A-3L.

As described herein, the VC waveguide 1101 can include an inner core(e.g., an inner vanishing core) 1110, an outer core 1120, and an outercladding 1130 with refractive indices N-1, N-2, and N-3 respectively. Asshown in FIG. 7 , the VC waveguide 1101 can also include a secondaryouter core 1122 (e.g., between the outer core 1120 and the outercladding 1130) having refractive index N-2A. As the outer core 1120 canlongitudinally surround the inner core 1110, the secondary outer core1122 can longitudinally surround the outer core 1120 with the outercladding 1130 longitudinally surrounding the secondary outer core 1122.In various embodiments, the relationship between the refractive indicesof the inner core 1110, outer core 1120, secondary outer core 1122, andouter cladding 1130 can advantageously be N-1>N-2>N2-A>N-3. With such arelationship, each surrounding layer can serve as an effective claddingto the layers within it (e.g., the outer core 1120 can serve as aneffective cladding to the inner core 1110, and the secondary outer core1122 can serve as an effective cladding to the outer core 1120). Hence,the use of the secondary outer core 1122 can provide an additional setof core and cladding.

By including the secondary outer core 1122 with a refractive index N-2A,certain embodiments can achieve a higher NA (e.g., compared to withoutthe secondary outer core 1122). In various embodiments, the difference(N-2A minus N-3) can be larger than the differences (N-2 minus N-2A) or(N-1 minus N-2) to result in a relatively high NA. Increasing NA canreduce the MFD, allowing for the channels (e.g., waveguides 1100) to becloser to each other (e.g., closer spacing between the waveguides 1100)without compromising crosstalk. Accordingly, the coupler array 450 canbe reduced further in cross section (e.g., compared to without thesecondary outer core 1122) to provide a reduced region when light isguided by the secondary outer core 1122. By providing a reduced regionbetween the first end 1010 and the second end 1020, certain embodimentscan include a flexible portion 1050 which can be more flexible than theregions proximal to the first end 1010 and the second end 1020.

For example, the inner core 1110 size, the outer core 1120 size, and thespacing between the waveguides 1100 can reduce (e.g., simultaneously andgradually in some instances) along the optical element 1000 from thefirst end 1010 to the intermediate location 1040 such that at theintermediate location 1040, the inner core 1110 size is insufficient toguide light therethrough and the outer core 1120 size is sufficient toguide at least one optical mode. In certain embodiments, each waveguide1100 can have a capacity for at least one optical mode (e.g., singlemode or multi-mode). For example, at the first end 1010, the VCwaveguide 1101 can support a number of spatial modes (M1) within theinner core 1110. At the intermediate location 1040, in variousembodiments, the inner core 1110 may no longer be able to support allthe M1 modes (e.g., cannot support light propagation). However, in somesuch embodiments, at the intermediate location 1040, the outer core 1120can be able to support all the M1 modes (and in some cases, able tosupport additional modes). In this example, light traveling within theinner core 1110 from the first end 1010 to the intermediate location1040 can escape from the inner core 1110 into the outer core 1120 suchthat light can propagate within both the inner core 1110 and outer core1120.

In addition, the outer core 1120 size, the secondary outer core 1122size, and the spacing between the waveguides 1100 can reduce (e.g.,simultaneously and gradually in some instances) along said opticalelement 1000, for example, from the intermediate location 1040 to theflexible portion 1050 such that at the flexible portion 1050, the outercore 1120 size is insufficient to guide light therethrough and thesecondary outer core 1122 size is sufficient to guide at least oneoptical mode therethrough. In certain embodiments, at the intermediatelocation 1040, the VC waveguide 1101 can support all the M1 modes withinthe outer core 1120. At the flexible portion 1050, in variousembodiments, the outer core 1120 may be no longer able to support allthe M1 modes (e.g., cannot support light propagation). However, in somesuch embodiments, at the flexible portion 1050, the secondary outer core1122 can be able to support all the M1 modes (and in some cases, able tosupport additional modes). In this example, light traveling within theouter core 1120 from the intermediate location 1040 to the flexibleportion 1050 can escape from the outer core 1120 into the secondaryouter core 1122 such that light can propagate within the inner core1110, the outer core 1120, and secondary outer core 1122.

Furthermore, the outer core 1120 size, the secondary outer core 1122size, and the spacing between the waveguides 1100 can expand (e.g.,simultaneously and gradually in some instances) along the opticalelement 1000 from the flexible portion 1050 to the second end 1020 suchthat at the second end 1020, the secondary outer core 1122 size isinsufficient to guide light therethrough and the outer core 1120 size issufficient to guide at least one optical mode therethrough. In certainembodiments, at the second end 1020, in various embodiments, thesecondary outer core 1122 may no longer be able to support all the M1modes (e.g., cannot support light propagation). However, in some suchembodiments, at the second end 1020, the outer core 1120 can be able tosupport all the M1 modes (and in some cases, able to support additionalmodes). In this example, light traveling within the secondary outer core1122 from the flexible portion 1050 to the second end 1020 can returnand propagate only within the inner core 1110 and the outer core 1120.

It would be appreciated that light travelling from the second end 1020to the first end 1010 can behave in the reverse manner. For example, theouter core 1120 size, the secondary outer core 1122 size, and spacingbetween the waveguides 1100 can reduce (e.g., simultaneously andgradually in some instances) along the optical element 1000 from thesecond end 1020 to the flexible portion 1050 such that at the flexibleportion 1050, the outer core 1120 size is insufficient to guide lighttherethrough and the secondary outer core 1122 size is sufficient toguide at least one optical mode therethrough.

The reduction in cross-sectional core and cladding sizes canadvantageously provide rigidity and flexibility in a coupler array 450.Since optical fibers 2000 and/or an optical device 3000 can be fused tothe ends 1010, 1020 of the coupler array 450, rigidity at the first 1010and second 1020 ends can be desirable. However, it can also be desirablefor coupler arrays to be flexible so that they can bend to connect withlow profile integrated circuits. In certain embodiments, the flexibleportion 1050 between the first 1010 and second 1020 ends can allow thefirst 1010 and second 1020 ends to be relatively rigid, while providingthe flexible portion 1050 therebetween. The flexible portion can extendover a length of the optical element 1000 and can mechanically isolatethe first 1010 and second 1020 ends. For example, the flexible portion1050 can mechanically isolate the first end 1010 from a region betweenthe flexible portion 1050 and the second end 1020. As another example,the flexible portion 1050 can mechanically isolate the second end 1020from a region between the first end 1010 and the flexible portion 1050.Such mechanical isolation can provide stability to the first 1010 andsecond 1020 ends, e.g., with respect to environmental fluctuations,including temperature variations and mechanical shock and vibration. Thelength of the flexible portion 1050 is not particularly limited and candepend on the application. In some examples, the length can be in arange from 2 to 7 mm, from 3 to 8 mm, from 5 to 10 mm, from 7 to 12 mm,from 8 to 15 mm, any combination of these ranges, or any range formedfrom any values from 2 to 20 mm (e.g., 3 to 13 mm, 4 to 14 mm, 5 to 17mm, etc.). In other examples, the length of the flexible portion 1050can be shorter or longer.

At the same time, the flexible portion 1050 can provide flexibility. Inmany instances, the flexible portion 1050 can have a substantiallysimilar cross-sectional size (e.g., the cross-sectional size of thewaveguides 1100) extending over the length of the flexible portion 1050.In certain embodiments, the cross-section size at the flexible portion1050 can comprise a smaller cross-sectional size than thecross-sectional size at the first 1010 and second 1020 ends. Having asmaller cross-sectional size, this flexible portion 1050 can be moreflexible than a region proximal to the first 1010 and second 1020 ends.The smaller cross-sectional size can result from the reduction in coreand cladding sizes. An optional etching post-process may be desirable tofurther reduce the diameter of the flexible length of the flexible PROFAcoupler 450.

In some embodiments, the flexible portion 1050 can be more flexible thana standard SMF 28 fiber. In some embodiments, the flexible portion 1050can bend at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees,110 degrees, 120 degrees, or at least any value therebetween. In someembodiments, the flexible portion 1050 can bend in a range formed by anyof these values, e.g., from 45 to 55 degrees, from 50 to 60 degrees,from 60 to 70 degrees, from 70 to 80 degrees, from 80 to 90 degrees,from 90 to 100 degrees, from 100 to 110 degrees, from 110 to 120degrees, or any combinations of these ranges, or any ranges formed byany values within these ranges (e.g., from 50 to 65 degrees, from 50 to85 degrees, from 65 to 90 degrees, etc.) In other embodiments, theflexible portion 1050 can bend more or less than these values. Asdescribed herein, in various applications, the flexible portion 1050might not bend in use, however the flexibility can be desired fordecoupling the first 1010 or second 1020 end from other parts of thecoupler array 450.

The coupler array 450 can include a coupler housing structure 1060. Forexample, the coupler housing structure 1060 can include a common singlecoupler housing structure. In certain embodiments, the coupler housingstructure 1060 can include a medium 1140 (e.g., having a refractiveindex N-4) surrounding the waveguides 1100. In some instances, N-4 isgreater than N-3. In other examples, N-4 is equal to N-3. The medium1140 can include any medium as described herein (e.g., pure-silica). Themedium can also include glass such that the coupler array 450 can be anall-glass coupler array. The waveguides 1100 can be embedded within themedium 1040 of the housing structure 1060. In some examples, a totalvolume of the medium 1140 of the coupler housing structure 1060 can begreater than a total volume of all the inner and outer cores 1110, 1120,1122 of the VC waveguides confined within the coupler housing structure1060.

In some embodiments, each waveguide can couple to the optical fibers2000 and/or optical device 3000 at a location inside, outside, or at aboundary region of the coupler housing structure 1060, e.g., as shown inFIGS. 1A to 2D. Because the optical fibers 2000 and optical device 3000can be different at each end, the first end 1010 and the second end 1020can each be configured for the optical fibers 2000 or optical device3000 with which it is coupled. For example, the MFD of the VC waveguideat the first 1010 and/or second 1020 ends can be configured (e.g., usingthe sizes of the cores) to match or substantially match the MFD of theoptical fiber 2000 or optical device 3000 with which it is coupled. Inaddition, the NA of the VC waveguide at the first 1010 and/or second1020 ends can be configured (e.g., using the refractive indices) tomatch or substantially match the NA of the optical fiber 2000 or opticaldevice 3000 with which it is coupled. The refractive indices can bemodified in any way known in the art (e.g., doping the waveguide glass)or yet to be developed. In various embodiments, as described herein, thedifference (N-1 minus N-2) can be greater than the difference (N-2 minusN-2A) such that the NA at the first end 1010 is greater than the NA atthe second end 1020. In other embodiments, the difference (N-1 minusN-2) can be less than the difference (N-2 minus N-2A) such that the NAat the first end 1010 is less than the NA at the second end 1020. In yetother embodiments, the difference (N-1 minus N-2) can be equal to (N-2minus N-2A) such that the NA at the first end 1010 is equal to the NA atthe second end 1020. The VC waveguide can include any of the fiber typesdescribed herein including but not limited to a single mode fiber, amulti-mode fiber, and/or a polarization maintaining fiber.

The core and cladding (1110, 1120, 1122, 1130) sizes (e.g., outercross-sectional diameters if circular or outer cross-sectionaldimensions if not circular) are not particularly limited. In someembodiments, the inner 1110 and/or outer 1120 core sizes can be in arange from 1 to 3 microns, from 2 to 5 microns, from 4 to 8 microns,from 5 to 10 microns, any combination of these ranges, or any rangeformed from any values from 1 to 10 microns (e.g., 2 to 8 microns, 3 to9 microns, etc.). However, the sizes can be greater or less. Forexample, the inner 1110 and/or outer 1120 core sizes can range fromsubmicrons to many microns, to tens of microns, to hundreds of micronsdepending, for example, on the wavelength and/or number of modesdesired.

In addition, the difference in the refractive indices (e.g., between N-1and N-2, between N-2 and N-2A, and/or between N-2A and N-3) is notparticularly limited. In some examples, the index difference can be in arange from 1.5×10⁻³ to 2.5×10⁻³, from 1.7×10⁻³ to 2.3×10⁻³, from1.8×10⁻³ to 2.2×10⁻³, from 1.9×10⁻³ to 2.1×10⁻³, from 1.5×10⁻³ to1.7×10⁻³, from 1.7×10⁻³ to 1.9×10⁻³, from 1.9×10⁻³ to 2.1×10⁻³, from2.1×10⁻³ to 2.3×10⁻³, from 2.3×10⁻³ to 2.5×10⁻³, any combination ofthese ranges, or any range formed from any values from 1.5×10⁻³ to2.5×10⁻³. In other examples, the index difference can be greater orless.

As described herein, the optical device 3000 can include a PIC. The PICcan include an array of VGCs. Also, as described in U.S. PatentApplication Publication 2012/0257857, entitled “HIGH DENSITY OPTICALPACKAGING HEADER APPARATUS”, which is hereby incorporated herein in itsentirety, multiple flexible PROFA couplers (such as the coupler 450),each having multiple optical channels, can be combined together toadvantageously form an optical multi-port input/output (IO) interface.As such, an optical multi-port 10 interface can include a plurality ofoptical coupler arrays, at least one of the optical coupler arrays caninclude an optical coupler array 450 as described herein.

With reference now to FIG. 8 and FIG. 9 , example cross sectional viewsof the housing structure at a proximity to a first end of a multichanneloptical coupler array are shown. The cross-sectional view is orthogonalto the longitudinal direction or length of the optical coupler array.Some such configurations may have improved cross sectional or transverse(or lateral) positioning of waveguides at the first end allowing forself-aligning waveguide arrangement at a close proximity to a first end(e.g., hexagonal close packed arrangement in a housing structure havingcircular (as shown in FIG. 8 ) or hexagonal inner cross section) andimproved (precise or near precise in some cases) cross sectionalpositioning of the waveguides at a second end. Such configurations mayalso provide alignment during manufacturing such that the crosssectional positioning of the waveguides at a second end may be moreprecisely disposed as desired.

Although various features of the example optical coupler arrays may bedescribed with respect to FIGS. 8 and 9 , any feature described above(for example, in connection with any of the figures or embodimentsdescribe above) can be implemented in any combination with amultichannel optical coupler array. For example, any of the featuresdescribed with respect to FIGS. 1A-5 and 7 may be utilized in amultichannel optical coupler array and may be combined with any featuredescribed with respect to FIGS. 8 and 9 .

For example, referring to the example embodiments shown in FIGS. 1A-2D,there are two ends of the coupler array: a first (larger) end, and asecond (smaller) end. The two ends are spaced apart in the longitudinaldirection (along the z direction). For example, in FIG. 1A, the firstend is proximate to position B and the second end is proximate topositions C and D.

In certain embodiments, one of the functions of the first end (proximateto position B) is to encapsulate the waveguides 30A, 32A-1, 32A-2 withincreased or approximate positioning accuracy. For example, the couplerhousing structure 14A at a proximity to the first end (proximate toposition B) may encapsulate, e.g., circumferentially surround a portionof the length of the waveguides 30A, 32A-1, 32A-2, but not necessarilycompletely enclose the ends of the waveguides 30A, 32A-1, 32A-2. In somesuch instances, the waveguides 30A, 32A-1, 32A-2 may or may not extend(e.g., longitudinally) outside the coupler housing structure 14A. InFIG. 1A, proximate the first end, the end of waveguide 30A is disposedwithin the coupler housing structure 14A, but the ends of waveguides32A-1 and 32A-2 extend, e.g., longitudinally (in a direction parallel tothe z-direction) outside of the coupler housing structure 14A. In FIG.2B, proximate the first end, the ends of waveguides 130B-1, 130B-2 aredisposed at an outer cross sectional boundary region of the couplerhousing structure 14A and do not extend, e.g., longitudinally (in adirection parallel to the z-direction) outside of the coupler housingstructure 14A.

In various embodiments, one of the functions of the second end(proximate to positions C and D) is to have the waveguides 30A, 32A-1,32A-2 embedded in a housing structure (e.g., a common housing structurein some instances) with improved (precise or near precise in some cases)cross sectional positioning. For example, the waveguides 30A, 32A-1,32A-2 at a proximity to the second end (proximate to positions C and D)may be embedded, e.g., be circumferentially surrounded by the contiguouscoupler housing structure 14A. In FIG. 1A, proximate the second end, theends of waveguides 30A, 32A-1, 32A-2 are longitudinally disposed at anouter cross sectional boundary region of the coupler housing structure14A. In some embodiments, proximate the second end, one or more ends ofthe waveguides may be disposed within or may longitudinally extendoutside the coupler housing structure 14A.

To achieve improved positioning, some embodiments can include theexample cross sectional configuration of the housing structure shown inFIG. 8 at a proximity to the first end. The cross section is orthogonalto the longitudinal direction or length of the optical coupler array. Asshown in FIG. 8 , the coupler array 800 can include a housing structure801 having a transverse (or lateral) configuration of a ring surroundingthe plurality of longitudinal waveguides 805 at a close longitudinalproximity to the first end. A gap, such as an air gap, may separate theplurality of longitudinal waveguides 805 from the surrounding ring. Somesuch configurations may allow for self-aligning waveguide arrangement ata close proximity to a first end (e.g., hexagonal close packedarrangement in a housing structure having circular (as shown in FIG. 8 )or hexagonal inner cross section)

In an example configuration shown in FIG. 8 , the waveguides 805 are ina hexagonal arrangement. Other arrangements are possible, e.g., square,rectangular, etc.

The ring may have an inner cross section 801 a (in the transversedirection, i.e., orthogonal to the longitudinal direction or length ofthe optical coupler array) that is circular or non-circular. Forexample, the inner cross section 801 a may be circular, elliptical,D-shaped, square, rectangular, hexagonal, pentagonal, octagonal, otherpolygonal shape, etc. The inner cross section 801 a does not necessarilyfollow the arrangement of the waveguides 805. For example, fourwaveguides arranged in a square arrangement can be confined in an innercircular cross section. As another example, as shown in FIG. 8 , theinner cross section 801 a is circular, while the waveguides 805 arehexagonally arranged. In some embodiments, a circular inner crosssection, as shown in FIG. 8 , may be a preferred shape, which can allowfor a close-pack hexagonal arrangement. Also, other inner crosssectional shapes may also be used, such as square or rectangular, whichcan allow for non-hexagonal waveguide arrangements. In some instances,the inner cross section 801 a may be similar as the arrangement of thewaveguides 805 to reduce empty space. For example, for waveguides 805 ina hexagonal arrangement, the inner cross section 801 a of the ring maybe hexagonal to reduce empty space between the inner cross section 801 aand the waveguides 805.

The outer cross section 801 b (in the transverse direction, e.g.,orthogonal to the longitudinal direction or length of the opticalcoupler array) may be circular or non-circular. For example, the outercross section 801 b may be circular, elliptical, hexagonal, D-shaped(e.g., to provide for passive axial alignment of the coupler since theflat surface allow for an easy rotational alignment), square,rectangular, pentagonal, octagonal, other polygonal shape, etc. In FIG.8 , the outer cross section 801 b (e.g., circular) follows the shape ofthe inner cross section 801 a (e.g., circular). However, in someembodiments, the outer cross section 801 b need not be similar as theinner cross section 801 a. One of the functions of the inner crosssectional shape is to allow for an improvement in the transversepositional accuracy at the proximity to the second end, while one of thefunctions of the outer cross sectional shape is to allow for a passiveaxial alignment of the coupler (e.g., the alignment can be done withoutlaunching light into the coupler). In some configurations it may bepreferred to substantially preserve the outer cross sectional shape fromthe first end to the second end to facilitate the passive alignment atone of the ends or at both ends of the coupler array.

FIG. 9 shows another example cross sectional configuration of thehousing structure at a proximity to the first end. As shown in FIG. 9 ,the coupler array 850 can include a housing structure 851 having aconfiguration of a structure (e.g., a contiguous structure in somecases) with a plurality of holes 852. At least one of the holes 852 maycontain at least one of the longitudinal waveguides 855. A gap, such asan air gap, may separate the plurality of longitudinal waveguides 855from the surrounding housing structure 851. Similarly to the descriptionrelated to the example shown in FIG. 8 , the outer cross section may becircular, elliptical, hexagonal, D-shaped, square, rectangular,pentagonal, octagonal, other polygonal shape, etc. Some of suchconfigurations may allow for passive alignment at one of the ends or atboth ends of the coupler array. While the example configuration shown inFIG. 8 may allow for simpler fabrication in some cases, the exampleconfiguration shown in FIG. 9 may allow for arbitrary transversewaveguide positioning.

FIG. 9 shows an example configuration with six holes 852, yet othernumber of holes is possible. The holes 852 in this example configurationmay be isolated or some or even all holes 852 may be connected. Forexample, as shown in FIG. 9 , a first hole 852-1 is isolated from asecond hole 852-2. However, in some configurations, the first hole 852-1may be connected to at least one second hole 852-2. The arrangement ofthe holes 852 is shown as a 3×2 array, yet other arrangements arepossible. For example, the hole arrangement pattern may be hexagonal,square, rectangular, or defined by an XY array defining positions of theholes in the transverse plane.

FIG. 9 shows all the holes 852 with a waveguide 855 illustrated as avanishing core (VC) waveguide. However, while at least one of thewaveguide in this example is a VC waveguide, one or more of the holes852 may include a non-vanishing core (Non-VC) waveguide. The VC orNon-VC waveguide 855 can include any of the waveguides described herein,e.g., single mode fiber, multi-mode fiber, polarization maintainingfiber, etc. In some embodiments, one or more of the holes 852 may beempty, or populated with the other (e.g., non-waveguide) material, e.g.,to serve as fiducial marks. One or more of the holes 852 may bepopulated with a single waveguide 855 (in some preferred configurations)as shown in FIG. 9 or with multiple waveguides 855. Depending on thedesign, one or more of the holes 852 may be identical or different thananother hole 852 to accommodate, for example, waveguides 855 ofdifferent shapes and dimensions (e.g., cross sectional shapes,diameters, major/minor elliptical dimensions, etc.). The cross sectionsof the holes 852 may be circular or non-circular. For example, the crosssection may be circular, elliptical, hexagonal or D-shaped (e.g., toprovide for passive axial alignment of polarization maintaining (PM)channels), square, rectangular, pentagonal, octagonal, other polygonalshape, etc. As illustrated, in many cases, the cross section of the hole852 at close proximity to the first end is larger than the cross sectionof the waveguides 855 such that a gap is disposed between an innersurface 851 a of the coupler housing structure 851 and the waveguide855.

The coupler housing structure (e.g., 801 in FIG. 8 or 851 in FIG. 9 )can include a medium from a wide range of materials as described herein.As also described herein, the medium of the coupler housing structure801, 851 can have refractive index (N-4). The medium can be atransversely contiguous medium. This can allow for a robust housingstructure with improved transverse positioning accuracy in someembodiments. In some embodiments, the total volume of the medium of thecoupler housing structure 801, 851 can be greater than a total volume ofall the inner and outer cores of the VC waveguides confined within thecoupler housing structure 801, 851 to provide that in some embodiments,all VC waveguides are reliably embedded in the housing structureallowing for stable performance).

In certain embodiments, the example configurations shown in FIG. 8 andFIG. 9 may allow for improved manufacturability of the devices withimproved cross sectional (transverse) positioning of the waveguidese.g., at the second end. This transverse position, may for example, bedefined in the x and/or y directions, while z is the direction along thelength coupler array (e.g., from the first end to the second end). Invarious fabrication approaches, the assembly, comprising the waveguides(e.g., 805 in FIGS. 8 and 855 in FIG. 9 ) and coupler housing structure(e.g., 801 in FIG. 8 or 851 in FIG. 9 ), may be heated and drawn to forma second end as shown in the lateral cross sectional views shown inFIGS. 3A-3L. Referring to FIG. 8 , the waveguides 805 can be insertedinto the coupler housing structure 801 having a configuration of a ring(in the cross section orthogonal to the longitudinal direction or lengthof the optical coupler array, e.g., in the x-y plane shown). Asdescribed above, a gap such as an air gap can be disposed between thecoupler housing structure 801 and the waveguide 805 to permit lateralmovement (in x and/or y directions) of the waveguide with respect to thecoupler housing structure 801. Referring to FIG. 9 , one or morewaveguides 855 can be inserted into the coupler housing structure 851having a plurality of holes 852 (e.g., as seen in the cross sectionorthogonal to the longitudinal direction or length of the opticalcoupler array, e.g., in the x-y plane shown) where the waveguides 855can be passively aligned within the housing structure 851. A gap such asan air gap can be disposed between the coupler housing structure 851 andthe waveguide 855 to permit transverse movement (in x and/or ydirections) of the waveguide with respect to the coupler housingstructure 851. In the case of close packed waveguide arrangement (e.g.,hexagonal), this ability to move can result in more precise crosssectional positioning at the second end after manufacturing.

Referring to FIG. 1A, the coupler array can include a plurality oflongitudinal waveguides 30A, 32A-1, 32A-2 with at least one VC waveguide30A having an inner core 20A and an outer core 22A. The inner core 20A,the outer core 22A, and the spacing between the plurality of waveguides30A, 32A-1, 32A-2 can reduce (e.g., simultaneously and gradually in somecases) from the first end (proximate to position B) to the second end(proximate to positions C and D), e.g., from S-1 to S-2. In variousembodiments, the cross sectional configuration at the first end(proximate position B) is shown as in FIG. 8 or FIG. 9 , while the crosssectional configuration at the second end (proximate positions C and D)can be shown in FIGS. 3A-3L or FIG. 7 . In some embodiments, proximateto the second end, there is substantially no gap between the couplerhousing structure and the waveguides, some gaps being filled by housingmaterial and some gaps being filled by waveguide cladding material. As aresult of the described cross sectional configuration at the first end,the cross sectional or transverse positioning of the waveguides at thesecond end can be improved. The waveguides at the second end can thus beproperly aligned in the transverse direction (e.g., x and/or ydirection) with an optical device.

With reference now to FIG. 10 and FIG. 11 , further example embodimentsof optical coupler arrays 4000, 5000 are shown. The coupler arrays 4000,5000 can be configured to couple to and from a plurality of opticalfibers, such as to and from optical fibers with different mode fieldsand/or core sizes. In some instances, the coupler arrays 4000, 5000 canbe configured to provide coupling between a set of individual isolatedoptical fibers 2000 and an optical device 3000 having at least oneoptical channel allowing for propagation of more than one optical mode.In some preferred embodiments, all isolated optical fibers 2000 can beidentical (or some different in some instances) and the optical device3000 can include at least one few-mode fiber, multimode fiber, multicoresingle mode fiber, multicore few-mode fiber, and/or multicore multimodefiber. Compared to certain embodiments described herein with respect toFIGS. 1A-5 , various embodiments 4000, 5000 can include a furtherreduction of the taper diameter, which can allow light to escape theouter core 4120, 5120 and propagate in a combined waveguide 4150, 5150,formed by at least two neighboring cores. Accordingly, variousembodiments described herein can be configured to optically couplebetween fibers with dissimilar mode fields and/or core shapes or sizes.Advantageously, some embodiments of the coupler arrays can improveand/or optimize optical coupling between one or more of single modefibers, few-mode fibers, multimode fibers, multicore single mode fibers,multicore few-mode fibers, and/or multicore multimode fibers.

Although various features of the example coupler arrays will now bedescribed with respect to FIGS. 10 and 11 , any described feature can beimplemented in any combination with the coupler arrays described withrespect to FIGS. 1A-5 and 7 . Further, any feature described withrespect to FIGS. 1A-5 and 7 may be combined with any feature describedwith respect to FIGS. 10 and 11 . For instance, the example couplerarrays 4000, 5000 are illustrated utilizing housing structures 4060,5060 similar to the housing structures 801, 851 shown in FIGS. 8-9 . Inthese examples, the cross sectional configuration of the housingstructure 4060, 5060 may include a structure with a plurality of holes(e.g., multi-hole) as shown in FIG. 10 , or may include one hole (e.g.,single-hole surrounded by a ring), as shown in FIG. 11 . However, otherhousing structures can also be used. For example, the housing structuresdescribed with respect to FIGS. 1A-5 and 7 may be used.

Referring to FIG. 10 , certain embodiments of a multichannel opticalcoupler array 4000 can include an elongated optical element 4001 havinga first end 4010, an intermediate location or cross section 4050, and asecond end 4020. The optical element 4001 can include a coupler housingstructure 4060 and a plurality of longitudinal waveguides 4100 disposedin the housing structure 4060. The waveguides 4100 can be arranged withrespect to one another in a cross-sectional geometric waveguidearrangement. In FIG. 10 , the example cross-sectional geometricwaveguide arrangements of the waveguides 4100 for the first end 4010,the intermediate cross section 4050, and the second end 4020 are shown.As illustrated by the shaded regions within the cross sections and aswill be described herein, light can be guided through the opticalelement 4001 from the first end 4010, through the intermediate crosssection 4050, and to the second end 4020.

As shown in FIG. 10 , proximally (e.g. proximately) to the first end4010, the housing structure 4060 (e.g., a common single coupler housingstructure in some cases) can have a cross sectional configuration of astructure (e.g., transversely contiguous structure in some cases) with aplurality of holes 4062. FIG. 10 shows an example configuration withthree circular holes 4062-1, 4062-2, 4062-3. However, the shape of theholes, number of holes, and/or arrangement of the holes are notparticularly limited and can include any other shape, number, and/orarrangement including those described with respect to FIG. 9 . At leastone of the holes 4062 may contain at least one of the longitudinalwaveguides 4100. A gap, such as an air gap, may separate the pluralityof longitudinal waveguides 4100 from the surrounding housing structure4060 proximally to the first end 4010. In some embodiments, there may besubstantially no gap between the coupler housing structure 4060 and thewaveguides 4100 at the intermediate location 4050 and/or at the secondend 4020. For example, one or more gaps may be filled by housingmaterial and/or waveguide cladding material. As described herein, insome embodiments, proximate to the first end 4010, there may be a gapbetween the coupler housing structure 4060 and the waveguides 4100, butproximate to the second end 4020, there may be substantially no gapbetween the coupler housing structure 4060 and the waveguides 4100 (orvice versa). In some embodiments, there may be substantially no gapbetween the coupler housing structure 4060 and the waveguides 4100proximate the first end 4010, the intermediate location 4050, and/or atthe second end 4020.

As described herein, the coupler array 4000 can be operable to opticallycouple with a plurality of optical fibers 2000 and/or with an opticaldevice 3000. The coupler array 4000 can couple with the optical fibers2000 via the plurality of waveguides 4100 proximate the first end 4010(e.g., via a fusion splice 2001), and/or with the optical device 3000via the plurality of waveguides 4100 proximate the second end 4020(e.g., via a fusion splice not shown). In FIG. 10 , three waveguides4100 are shown in each of the three holes 4062-1, 4062-2, 4062-3.However, any number of waveguides 4100 for each of the holes 4062 can beused. In some embodiments, the number of waveguides 4100 may equal thenumber of optical fibers 2000 (e.g., 9 waveguides to couple with 9optical fibers). In some other embodiments, the number of waveguides4100 in at least one hole may equal the number of optical modessupported by a corresponding few-mode or multi-mode waveguide of thedevice 3000 (e.g. 3 waveguides in each of 3 holes to couple with three3-mode cores of a multicore fiber). In various embodiments, thewaveguides 4100 can be positioned within each hole 4062 at a spacing(e.g., predetermined in some instances) from one another. In somepreferred embodiments of the multi-hole configuration, the individualholes 4062-1, 4062-2, 4062-3 may contain all the waveguides (e.g.,fibers) intended to couple to at least one particular core of afew-mode, multimode and/or multicore fiber of an optical device. In someother embodiments, one or more additional fibers and/or dummy fibers(e.g., which might not guide light) may be utilized to create aparticular geometrical arrangement of the active, light-guiding fiberwaveguides.

In various embodiments, the plurality of waveguides 4100 can have acapacity for at least one optical mode (e.g., a predetermined mode fieldprofile in some cases). The plurality of waveguides 4100 can include atleast one vanishing core (VC) waveguide 4101. FIG. 10 illustrates all ofthe waveguides 4100 as VC waveguides. However, one or more Non-VCwaveguides may also be used. As described herein, the VC waveguide 4101can include an inner core (e.g., an inner vanishing core) 4110, an outercore 4120, and an outer cladding 4130 with refractive indices N-1, N-2,and N-3 respectively. The outer core 4120 can longitudinally surroundthe inner core 4110, and the outer cladding 4130 can longitudinallysurrounding the outer core 4120. As described herein, the relativemagnitude relationship between the refractive indices of the inner core4110, outer core 4120, and the outer cladding 4130 can advantageously beN-1>N-2>N-3.

In various embodiments, the housing structure 4060 can surround thewaveguides 4100. The coupler housing structure 4060 can include a medium4140 having an index of refraction N-4. The medium 4140 can include anyof those described herein. In some instances, a total volume of themedium 4140 of the coupler housing structure 4060 can be greater than atotal volume of all the inner and outer cores 4110, 4120 of the VCwaveguides confined within the coupler housing structure 4060. In someexamples, the waveguides 4100 may be embedded in the housing structure4060 (e.g., proximate the second end 4020).

In certain embodiments, the inner core 4110 waveguide dimensions, theouter core 4120 waveguide dimensions, refractive indices, and/ornumerical apertures (NAs) are selected to increase and/or optimizecoupling to the individual fibers 2000. In various embodiments, theouter core 4120 waveguide dimensions, refractive indices, NAs, and/orthe cladding 4130 dimensions are selected to increase and/or optimizecoupling to the optical device 3000. Various embodiments describedherein can also include reflection reduction features of thepitch-reducing optical fiber array described in U.S. application Ser.No. 14/677,810, entitled “OPTIMIZED CONFIGURABLE PITCH REDUCING OPTICALFIBER COUPLER ARRAY”, which is incorporated herein in its entirety. Forpolarization control, some of the outer cores 4120 can be made with anon-circular cross section (e.g., elliptical as shown in FIG. 10 ) and aparticular orientation of the outer cores 4120 can be used to increaseand/or optimize optical coupling. Various embodiments described hereincan also include features of any of the optical polarization modecouplers described in U.S. application Ser. No. 15/617,684, entitled“CONFIGURABLE POLARIZATION MODE COUPLER”, which is incorporated hereinin its entirety.

In some embodiments, the inner core 4110 size, the outer core 4120 size,the cladding 4130 size, and/or the spacing between the waveguides 4100can reduce (e.g., simultaneously and gradually in some instances) alongthe optical element 4001 from the first end 4010 to an intermediatelocation or cross section 4050. In some embodiments, a predeterminedreduction profile may be used. In the example shown in FIG. 10 , at theintermediate location 4050, the inner core 4110 may be insufficient toguide light therethrough and the outer core 4120 may be sufficient toguide at least one optical mode (e.g., spatial mode).

In some embodiments, each core of a waveguide 4100 can have a capacityfor at least one optical mode (e.g., single mode, few-mode, ormulti-mode). For example, at the first end 4010, the VC waveguide 4101can support a number of spatial modes (M1) within the inner core 4110.At the intermediate location 4050, in various embodiments, the innercore 4110 may no longer be able to support all the M1 modes (e.g.,cannot support light propagation). However, in some such embodiments, atthe intermediate location 4050, the outer core 4120 can be able tosupport all the M1 modes (and in some cases, able to support additionalmodes). In this example, light traveling within the inner core 4110 fromthe first end 4010 to the intermediate location 4050 can escape from theinner core 4110 into the outer core 4120 such that light can propagatewithin the outer core 4120.

In some embodiments, the inner core 4110 size, the outer core 4120 size,the cladding 4130 size, and/or the spacing between the waveguides 4100can be further reduced (e.g., simultaneously and gradually in someinstances) along the optical element 4001 from the intermediate location4050 to the second end 4020. In the example shown in FIG. 10 , at thesecond end 4020, the outer core 4120 may be insufficient to guide lighttherethrough.

In certain embodiments, at the intermediate location 4050, the VCwaveguide 4101 can support all the M1 modes within the outer core 4120.At the second end 4020, the outer core 4120 may be no longer able tosupport all the M1 modes (e.g., cannot support light propagation).However, in some such embodiments, at the second end 4020, a combinedcore 4150 of at least two cores may be able to support all the M1 modesof all waveguides 4101 combined (and in some cases, able to supportadditional modes). In this example, light traveling within the outercore 4120 from the intermediate location 4050 to the second end 4020 canescape from the outer core 4120 into a combined waveguide 4150 formed byat least two outer cores (e.g., two or more neighboring cores) such thatlight can propagate within the combined cores. In the example shown inFIG. 10 , each of the combined waveguides 4150 is formed by three outercores. However, in some embodiments, the combined waveguides 4150 may beformed with another number of outer cores.

It would be appreciated that light travelling from the second end 4020to the first end 4010 can behave in the reverse manner. For example, insome embodiments, light can move from the combined waveguide 4150 formedby at least two neighboring outer cores into the at least one outer core4120 proximally to the intermediate cross section 4050, and can movefrom the outer core 4120 into corresponding inner core 4110 proximallyto the first end 4010. In the example shown in FIG. 10 , each of thecombined waveguides 4150 can support three propagation modes. Travellingfrom the second end 4020 to the first end 4010, each propagation modecan be coupled to a corresponding outer core 4120 proximally to theintermediate cross section 4050 and move from the outer core 4120 into acorresponding inner core 4110 proximally to the first end 4010.

Referring now to FIG. 11 , the example embodiment 5000 includes similarfeatures as the example embodiment 4000 shown in FIG. 10 . Onedifference is that the cross sectional configuration of the housingstructure 5060 includes a structure with a single hole 5062 instead of aplurality of holes 4062. Similar to the example embodiment 4000 shown inFIG. 10 , the optical element 5001 can include a coupler housingstructure 5060 (e.g., including a medium 5140) and a plurality oflongitudinal waveguides 5100 disposed in the housing structure 5060. Thewaveguides 5100 can be arranged with respect to one another in across-sectional geometric waveguide arrangement within the hole 5062. Asillustrated, light can be guided through the optical element 5001 fromthe first end 5010, through the intermediate cross section 5050, and tothe second end 5020.

As described herein, a gap may separate the plurality of longitudinalwaveguides 5100 from the surrounding housing structure 5060. In someembodiments, there may be substantially no gap between the couplerhousing structure 5060 and the waveguides 5100 proximate theintermediate location 5050 and/or the second end 5020. For example, inFIG. 11 , although a gap is shown proximate the second end 5020, inpreferred embodiments, there may be substantially no gap between thecoupler housing structure 5060 and the waveguides 5100. In someembodiments, there may be substantially no gap between the couplerhousing structure 5060 and the waveguides 5100 proximate the first end5010, the intermediate location 5050, and/or the second end 5020.

In various embodiments, the plurality of waveguides 5100 can include atleast one VC waveguide 5101. FIG. 11 illustrates all thirty seven of thewaveguides 5100 as VC waveguides 5101 in a hexagonal arrangement.However, any arrangement may be used. In addition, any number of VCwaveguides, Non-VC waveguides, and/or dummy fibers may be used. Asdescribed herein, one or more dummy fibers may be utilized to create aparticular geometrical arrangement of the active, light-guiding fiberwaveguides. As described herein, the VC waveguide 5101 can include aninner vanishing core 5110, an outer core 5120, and an outer cladding5130.

In certain embodiments, the inner core 5110 waveguide dimensions, theouter core 5120 waveguide dimensions, the cladding 5130 dimensions,refractive indices, and/or the numerical apertures (NAs) can be selectedto increase and/or optimize coupling to the individual fibers 2000and/or optical device 3000. In some embodiments, the inner core 5110size, the outer core 5120 size, the cladding 5130 size, and/or thespacing between the waveguides 5100 can reduce along the optical element5001 from the first end 5010 to the second end 5020. In the exampleshown in FIG. 11 , at the intermediate location 5050, the inner core5110 of certain waveguides 5100 may be insufficient to guide lighttherethrough and the outer core 5120 of certain waveguides 5100 may besufficient to guide at least one optical mode (e.g., spatial mode). Inthis example, proximate the second end 5020, the outer core 5120 may beinsufficient to guide light therethrough. Accordingly, in someembodiments, light traveling within the outer core 5120 from theintermediate location 5050 to the second end 5020 can escape from theouter core 5120 into a combined waveguide 5150 formed by at least twoouter cores (e.g., two or more neighboring cores) such that light canpropagate within the combined cores. In the example shown in FIG. 11 ,although each of the combined waveguides 5150 is formed by three outercores, the combined waveguides 5150 may be formed by another number ofouter cores. The remaining cores (e.g., cores of waveguides or dummyfibers) may or may not guide light. Light travelling from the second end5020 to the first end 5010 can behave in the reverse manner.

Space division multiplexing (SDM) can be used to overcome single fibercapacity limits. To allow deployment of multicore fiber (MCF), as one ofthe possible SDM implementations, development of fiber optic componentsproviding access to the individual cores of the MCFs is desirable. Thepresent application addresses some such components: adaptors betweenMCFs with different core patterns and/or add-drop multiplexers for MCFs.

As shown in FIGS. 12A-12C, both functions, combined or separately, maybe achieved with two individual fan-in/fan-out devices with the pigtailfiber spliced together as indicated by the stars. FIG. 12A shows singlechannel add-drop; FIG. 12B shows pattern adaptation; and FIG. 12C showscombined pattern adaptation and channel add-drop. Some considerations,however, are (1) high insertion loss, which can include a sum of twofan-out devices, (2) large size of the combined component, and (3) highcost of the assembly.

To address these factors, in the present disclosure, in variousimplementations, space division multiplexers can comprise adouble-tapered elongated optical element in which thepass-through-channels do not include splices and can provide low-lossconnections between two similar or dissimilar MCFs or other multichanneloptical devices. FIG. 13 is a schematic diagram of an exampledouble-tapered elongated optical coupler array. The coupler array 6000can include a housing structure 6005, a first end 6010, a middle portion6015, and a second end 6020. The coupler array 6000 can include a firsttapered portion 6030 and a second tapered portion 6040. The firsttapered portion 6030 can be located between the first end 6010 and themiddle portion 6015, and the second tapered portion 6040 can be locatedbetween the second end 6020 and the middle portion 6015. In variousdesigns, the housing structure 6005 can include the first and secondtapered portions 6030, 6040 and a connecting sleeve therebetween 6035.In FIG. 13 , the outer diameter of the coupler array 6000 is tapered upfrom the first end 6010 to the middle portion 6015, and is tapered downfrom the middle portion 6015 to the second end 6020. The coupler array6000 can include a plurality of spatial optical channels 6050. Forexample, the pass-through-channels may comprise vanishing corewaveguides (e.g., as described herein), or enlarged core waveguides(e.g., waveguides with core sizes larger than for standard opticalfiber), or other type waveguides allowing for up and down tapering withlight propagation preservation. The spatial optical channels 6050 (e.g.,via one or more through-channels) can be configured to optically couplea first optical device 6070 to a second optical device 6080. Forexample, at least one through-channel can be operable to couple (e.g.,directly couple) at least one optical channel of the first opticaldevice 6070 with at least one optical channel of the second opticaldevice 6080. In various instances, the through-channel can be embeddedin the housing structure 6005 at the first and/or second ends 6010,6020. In various designs, individual ones of the spatial opticalchannels 6050 (e.g., through-channels) do not include splices within thehousing structure 6005.

The first optical device 6070 and/or the second optical device 6080 caninclude a MCF or other multichannel optical device. The transversechannel patterns of the optical devices 6070, 6080 may be arbitrarilyconfigured as desired, for example, by an application. In someinstances, the transverse channel patterns of the optical devices 6070,6080 may be similar. In other instances, the transverse channel patternsof the optical devices 6070, 6080 may be dissimilar. For example, asshown in FIG. 13 , the transverse channel pattern can include two rowsof channels in one device 6070 and a circumferential channel pattern inthe other one 6080, and the pattern adaptation (e.g., converting onespatial pattern of channels to another different spatial pattern ofchannels) can be achieved. In some such designs, the spatial opticalchannels 6050 disposed within the housing 6005 can form transversechannel patterns at the first and second ends 6010, 6020, which can besimilar to the transverse channel patterns of the first and secondoptical devices 6070, 6080 respectively. For example, the first taperedportion 6030 can have a transverse channel pattern similar to thetransverse channel pattern of the first optical device 6070 and thesecond tapered portion 6040 can have a transverse channel patternsimilar to the transverse channel pattern of the second optical device6080.

In various implementations, the first tapered portion 6030 and/or thesecond tapered portion 6040 can include a tapered housing structure anda plurality of longitudinal waveguides (e.g., a portion of the spatialoptical channels 6050). Individual ones of the longitudinal waveguidescan be positioned at a spacing (e.g., predetermined in some cases) fromone another, can have a capacity for at least one optical mode (e.g., ofa predetermined mode field profile), and can be embedded in the taperedhousing structure proximally to the corresponding first or second end6010, 6020. At least one of the longitudinal waveguides can be thethrough-channel common for both the first and second tapered portions6030, 6040.

In some implementations, at least one through-channel can include avanishing core waveguide, e.g., as described herein. In someimplementations, at least one through-channel can include an enlargedcore waveguide, such as a waveguide with a core size larger than that ofa standard optical fiber. In some instances, the enlarged core waveguidecan include an enlarged core having a core refractive index (NCO). Theenlarged core can have a first enlarged core size (ECS-1) at the firstend 6010, a second enlarged core size (ECS-2) at the second end 6020,and an intermediate enlarged core size (ECS-IN) at the middle portion6015 therebetween. The enlarged core waveguide can also include an outercladding longitudinally surrounding the enlarged core. The outercladding can have a cladding refractive index (NCL). A relativemagnitude relationship between the refractive indices can include thefollowing magnitude relationship: (NCO>NCL). In some instances, thefirst enlarged core size (ECS-1) can be gradually increased from thefirst end 6010 to the middle portion 6015 and gradually reduced from themiddle portion 6015 to the second end 6020, e.g., in accordance with apredetermined profile along the housing structure 6005. In someinstances, the first and second enlarged core sizes (ECS-1 and ECS-2,respectively) and the refractive indices NCO and NCL can match (e.g.,selected to substantially match in some cases) waveguide properties ofat least one channel of the first and/or second optical devices, 6070,6080 respectively. In some instances, the intermediate enlarged coresize (ECS-IN) can have (e.g., selected to have in some cases) largermode volume than at least one channel of the first and second opticaldevices 6070, 6080, such that light traveling from the first end 6010 tothe middle portion 6015 then from middle portion 6015 to the second end6020 keeps propagating in at least one lowest order mode.

FIGS. 14-15 are schematic diagrams of other example double-taperedelongated optical coupler arrays configured to optically couple a firstoptical device to a second optical device. In some implementations, thecoupler array can be configured to provide access (e.g., direct access)to at least one optical channel of the first and/or second opticaldevice. Similar to the example coupler array 6000 in FIG. 13 , each ofthe optical coupler arrays 7000, 8000 in FIGS. 14-15 can include ahousing structure 7005, 8005; a first end 7010, 8010; a middle portion7015, 8015; a second end 7020, 8020; a first tapered portion 7030, 8030;and a second tapered portion 7040, 8040. In some designs, the housingstructure 7005, 8005 can be a single monolithic coupler housingstructure comprising the first tapered portion 7030, 8030; the middleportion 7015, 8015; and the second tapered portion 7040, 8040. Thespatial optical channels 7050, 8050 (e.g., via one or morethrough-channels) can be configured to optically couple a first opticaldevice 7070, 8070 to a second optical device 7080, 8080.

As shown in FIGS. 14-15 , an access region 7016, 8016 in the middleportion 7015, 8015 can allow the creation of an add-drop multiplexer,where one or two access channels (e.g., direct access channels) 7051,7052 in FIGS. 14 and 8051, 8052 in FIG. 15 (e.g., any type of waveguidesuch as standard optical fiber, a vanishing core waveguide, an enlargedcore waveguide, etc.) can be coupled (e.g., directly) to the opticaldevices 7070, 7080 in FIGS. 14 and 8070, 8080 in FIG. 15 at the firstand/or second ends of those access channels. For example, one or moreoptical waveguides can pass through the access region 7016, 8016 fromoutside space into the housing structure 7005, 8005 operable to provideaccess to at least one optical channel of the first optical device 7070,8070 or second optical device 7080, 8080. The optical waveguide (e.g.,an optical fiber) 7051, 7052, 8051, 8052 can have a first end disposedwithin the housing structure 7005, 8005 and a second end disposedoutside the housing structure 7005, 8005. For example, the first end ofthe optical waveguide 7051, 7052, 8051, 8052 can be disposed at thefirst end 7010 or second end 7020 of the housing structure 7005, 8005.The optical waveguide 7051, 7052, 8051, 8052 can exit the housingstructure 7005, 8005 through the middle portion 7015, 8015 of thehousing structure 7005, 8005.

As shown in FIGS. 14-15 , an access channel 7051, 8051 can be coupled tothe first optical device 7070, 8070 at the first end 7010, 8010 of thecoupler array 7000, 8000 and access channel 7052, 8052 can be coupled tothe second optical device 7080, 8080 at the second end 7020, 8020 of thecoupler array 7000, 8000. In some implementations, one channel 7051,8051 can serve as a “drop” channel to extract an optical signal from anSDM transmission line and another one 7052, 8052 can serve as an “add”channel to substitute the dropped signal with a new one. This add-dropfunctionality may be achieved without pattern adaptation, as shown inFIG. 14 (e.g., optical devices 7070, 7080 having similar transversechannel patterns), or with a pattern adaptation, e.g., if an accessregion 8016 is created in the connecting sleeve, as shown in FIG. 15(e.g., optical devices 8070, 8080 having dissimilar transverse channelpatterns). Although FIGS. 14-15 show examples with one “add” channel andone “drop” channel, some optical coupler arrays can be configured toprovide more than one “add” and/or “drop” channels. In addition, someoptical coupler arrays can be configured to provide only one or more“add” channels or only one or more “drop” channels.

In various implementations, at least one access optical channel 7051,7052, 8051, 8052 can be a vanishing core waveguide. For example, atleast one access optical channel 7051, 7052, 8051, 8052 may be operableto provide access to at least one optical channel of the first opticaldevice 7070, 8070 and/or the second optical device 7080, 8080 can be avanishing core waveguide. In some such instances, at least one accesschannel 7051, 7052, 8051, 8052 can also include a standard optical fiberfusion spliced to the access vanishing core waveguide with the splicelocation outside the housing structure 7005, 8005 in such a way that theaccess vanishing core waveguide passes through the access region 7015,8015 from outside space into the housing structure 7005, 8005. In someinstances, the splice location can be inside the housing structure 7005,8005 in such a way that the standard optical fiber passes through theaccess region 7015, 8015 from outside space into the housing structure7005, 8005.

Another application of the present disclosure can include fiber opticgyroscopes, where access to a single channel of the looped MCF isdesired. In some designs, two ends of the same span of MCF can becoupled to the first and second ends of the device shown in FIG. 14(e.g., forming a fiber loop in the fiber optic gyroscope). In variousimplementations, the MCF can have a circumferential core arrangementpattern, for example, numbered along the circumference: core number 1 orchannel 1, core number 2 or channel 2, . . . core number N or channel N.A connection orientation at the first end 7010 can provide coupling ofat least one access channel 7051 to core number 1, and a connectionorientation at the second end 7020 can provide coupling of core number 1via at least one through-channel to core number 2 at the first end 7010.Core number 2 can couple to core number 3, until core number N-1 iscoupled to core number N, which can be coupled to a second accesschannel 7052 at the second end 7020. For example, the MCF can be axiallytwisted, such that a light signal from the “drop” channel 7051 can becoupled to channel 1 of the MCF 7070 at the first end 7010. At thesecond end 7020, the light signal can be coupled to a through-channel ofthe spatial optical channels 7050, and, then the signal can be coupledto channel 2 of the MCF 7070 at the first end 7010. In this same manner,core number 2 can couple to core number 3 and so on, until core numberN-1 can be coupled to core number N, which can be finally coupled to the“add” channel 7052 at the second end 7020.

In various implementations, the housing structure may be glass, metal,or polymer, e.g., as desired by an application. The channels can beembedded in a portion of the housing structure. For example, thechannels can be embedding in the housing structure closer to the taperedend(s). In some instances, the channels can be embedded in 40%, 45%,50%, 55%, 60%, etc. (or any ranges formed by such values) of the taperedlength. In some designs, the channels can be embedded throughout thehousing structure. In some instances, there may be gaps (e.g., air orfilled with a filling material, or a combination of both) in the middleportion, for example, where the diameter is larger. The housingstructure can be substantially straight (e.g., straight or from 175° to185°). FIG. 16 is a schematic diagram of an optical coupler array 9000configured to optically couple a first optical device 9070 to a secondoptical device 9080. The coupler array 9000 can comprise a first end9010, a second end 9020, a first tapered portion 9030, and a secondtapered portion 9040. The coupler array 9000 can include a plurality ofspatial optical channels 9050 such as through-channels. As shown in FIG.16 , the housing structure 9005 (e.g., a middle portion) may be bent. Insome instances, the housing structure 9005 may include a flexibleportion that allows bending. In some instances, the housing structure9005 may include a rigidly bent portion. In various examples, thehousing structure 9005 may be bent at 90°, 100°, 110°, 120°, 130°, 140°,150°, 160°, 170°, etc. or any ranges formed by such values (e.g., 90° to170°, 90° to 150°, 90° to 130°, etc.). The bending may be 90 degrees asshown or 180 degrees as desired by an application. FIG. 16 shows anexample illustrating pattern adaptation. Also, add-drop multiplexing ora combination of the pattern adaptation and add-drop multiplexing may bedesired in either straight or bent configurations.

In some implementations, an optical coupler array can be configured tocouple with at least one optical device having at least one multimodeoptical channel. As an example, the multimode optical channel can be aninner cladding (e.g., for pump delivery) of a double-clad multicorefiber. In some instances, direct access can be provided to at least oneoptical mode of the multimode optical channel. FIG. 17 shows one suchexample of an optical coupler array 9100 coupling a first optical device9170 (e.g., single-clad MCF) at the first end 9110 to a second opticaldevice 9180 (e.g., double-clad MCF comprising an inner cladding 9181 andouter cladding 9182) at the second end 9120. Both of the coupledmultichannel optical devices 9170, 9180 can comprise multicore fiberswith the cores coupled via spatial optical channels 9150 such asthrough-channels (e.g., signal channels) and at least one access (e.g.,direct access) optical channel 9152 can comprise a multimode fibercoupled to at least one cladding mode of an inner cladding 9181 of thedouble-clad multicore fiber 9180.

In FIG. 17 , signal channels can be the pass-through channels of thespatial optical channels 9150 from the cores of the single-clad MCF 9170at the first end 9110 to the cores of the double-clad MCF 9180 at thesecond end 9120. The cores of the double-clad MCF 9180 can be singlemode, few mode, or multimode. The spatial optical channels 9150 (e.g.,through channels) can be multimode or vanishing core waveguides. Whendrawn, the cores of the optical coupler array 9100 at the second end9120 can be configured to match (e.g., substantially match) the cores ofthe double-clad MCF 9180. For example, in some implementations, thethrough channels can be vanishing core channels with single mode coresat the second end 9120 to match (e.g., substantially match) single modecores of the double-clad MCF 9180. In some instances, when the throughchannels are drawn, both ends (e.g., both tapered ends) may match thecores of the double-clad MCF 9180. For example, both ends of the throughchannels may be single mode (or few mode or multimode) to match thesingle mode (or few mode or multimode) cores of the double-clad MCF9180. An access channel 9152 through the access region 9116 can becoupled to the cladding modes. As illustrated in FIG. 17 , at least oneaccess channel 9152 can comprise a pump channel coupled to claddingmodes (e.g., to the inner cladding 9181) of the double-clad MCF 9180 atthe second end 9120. The double-clad MCF 9180 may be an active fiber,where one or more cores are doped with erbium or other active elementswhich are capable to amplify light when pumped by another light wave. Asillustrated, some implementations can have access to at least one pumpchannel at the access region 9116 (only one add channel shown) and thesignal channels can be the pass-through channels 9150. There may be adrop channel for at least one pump channel, which can be useful for pumprecycling at the other end of the double-clad MCF 9180. Add/drop pumpchannel(s) can be coupled to the cladding of the MCF and thecross-sectional location(s) need not match any MCF cores (e.g., coupledto the inner cladding of a double-clad multicore fiber). Similarly toFIG. 3E, pump channels may be conventional single core multimode pumpdelivery fibers, not vanishing core fibers. In some instances, the pumpchannels may be vanishing core fibers. The number of the pump channelsmay be one or more. There may be combinations of pump and signal addfunctionality, pump and signal drop functionality, and/or patternadaptation in one device.

To allow deployment of multicore fiber (MCF), as one of the possible SDMimplementations, development of fiber optic components providing accessto the individual cores of the MCFs at two wavelengths (e.g., pump andsignal wavelengths) can be desirable. The present application addressessome such components: a wavelength division-multiplexing (WDM) fanoutdevice and a pump-signal combiner for MCFs.

As shown in FIGS. 18A-18B, both functions, may be achieved with acombination of WDM device(s) with a fan-out (or fan-in) device and bycombining WDM device(s) with two fan-in/fan-out devices with the pigtailfiber spliced together as indicated by the stars. FIG. 18A shows aWDM-fanout device 1810, and FIG. 18B shows an MCF-WDM device 1820. InFIG. 18A, the WDM-fanout device 1810 includes a WDM device 1811, afan-out (or fan-in) device 1812, and a splice 1815 therebetween. The WDMdevice 1811 can be, for example, a wavelength combiner (e.g., a 980/1550combiner) which combines light at a first wavelength (Wavelength-1 orW-1) with light at a second wavelength (Wavelength-2 or W-2). Light atthe first wavelength can include signal light at 1550 nm and light atthe second wavelength can include pump light at 980 nm (or vice versa).Other examples are possible. The light at the first wavelength and thelight at the second wavelength can be combined into one of the cores1816 of an output MCF 1817. In some instances, the MCF 1817 can includeEr-doped fiber. In FIG. 18B, the MCF-WDM device 1820 includes a WDMdevice 1821 combined with two fan-in/fan-out devices 1822, 1824 withsplices 1825 therebetween. The MCF-WDM 1820 can include an input MCF1826 and an output MCF 1827. In some instances, the input MCF 1826 caninclude a transmission MCF. In some instances, the output MCF 1827 caninclude Er-doped fiber.

Some considerations, however, are (1) high insertion loss, which caninclude a sum of the WDM component and one or two fan-out devices, (2)the large size of the combined components, and (3) the high cost of theassembly.

To address these factors, in the present disclosure, in variousimplementations, the WDM function can be integrated into the spacedivision multiplexer. FIG. 19A shows a cross section of an exampleWDM-fanout device (e.g., a combined SDM-WDM) 1910. Light at onewavelength W-1 can be combined with light at another wavelength W-2 in acore of a MCF (e.g., into a core of a MCF coupled with the WDM-fanoutdevice 1910). For example, a signal (e.g., 1550 nm) or multiple signals(e.g., signals within the 1520-1570 nm C-band) and pump light (e.g., 980nm) can be combined in a core of a MCF. As another example, two signals(e.g., 1550 nm and 1310 nm) can be combined in a core of a MCF. In theexample shown in FIG. 19A, 1550 nm signal light can be combined with 980nm pump light in each core of a 4-core MCF. For example, in FIG. 19A,the WDM-fanout device 1910 includes 4 WDMs 1911A, 1911B, 1911C, 1911Drepresented by 4 pairs of adjacent waveguides. Each pair 1911A, 1911B,1911C, 1911D of adjacent waveguides includes a first waveguide for lightat a first wavelength (W-1) and second waveguide for light at a secondwavelength (W-2). The light at W-1 and the light at W-2 from each of theWDMs 1911A, 1911B, 1911C, 1911D can be combined into each core of a4-core MCF coupled with the WDM-fanout device 1910. Other designs canhave more or less WDMs and/or can be coupled to an MCF with more or lesscores. The number of WDMs and/or cores is not particularly limited.FIGS. 19B-19F show side views of various examples of the WDM-fanouttapered device 1910. In FIG. 19B, at the tapered end a compositewaveguide 1913 formed by outer cores of the signal and pump channelsguides the light at both wavelengths and is coupled to a correspondingcore 1916 of the MCF 1917. In some embodiments, the signal light can becoupled into a lowest order mode of the MCF core and the pump light canbe coupled into a set of modes with corresponding coupling coefficients.The wavelength combining is this case can be broadband, but the twowavelengths can be coupled to a set of modes with corresponding couplingcoefficients in the MCF core. For example, the signal light can becoupled into the lowest order mode of the output waveguide, and the pumplight can be coupled into a higher order mode (e.g., the 2^(nd) ordermode) of the output waveguide.

In various implementations, light of different wavelengths fromdifferent input waveguides (e.g., from the lowest order modes of theinput waveguides) can be combined into the same (e.g., lowest order)mode of the output waveguide. In the examples shown in FIG. 19C, FIG.19D, FIG. 19E, and FIG. 19F, no composite waveguide formed at the MCFinterface, but instead the MCF core 1926, 1936, 1946, 1956 is coupledonly with one of the input waveguides 1923, 1933, 1943, 1953. In theexamples shown in FIG. 19C and FIG. 19D, the wavelength combining can beachieved by creating a neck (e.g. neck coupling section) 1928, 1938 andin the examples shown in FIG. 19E and FIG. 19F, the wavelength combiningcan be achieved by a small waveguide separation section (e.g.substantially straight coupling section) 1948, 1958 at close proximityto the second end. Over these coupling sections 1928, 1938, the twowavelengths can be combined either in one (e.g., FIG. 19C) or the other(e.g., FIG. 19D) waveguide, which in turn, can be coupled to acorresponding MCF core 1926, 1936. Similarly, the examples shown in FIG.19E and FIG. 19F may be configured to couple MCF cores to the inner(e.g., as shown in FIG. 19F) or outer cores (e.g., as shown in FIG. 19E)at the tapered end. In various designs of the neck and substantiallystraight coupling section, the waveguides can be close together suchthat the light at one wavelength (e.g., W-1 or W-2) can remain in itswaveguide, while the light at the other wavelength can be coupled to theother waveguide. Both light signals at W-1 and W-2 can propagate in thesame output waveguide. Design parameters can include waveguideseparation and coupling section length. In various instances, thecoupling distance between waveguides can be configured to couple lightat one wavelength (e.g., W-1 or W-2) of at least one core mode of thewaveguide with at least one core mode of another waveguide whilecontinuing or preserving the propagation of light at the otherwavelength (e.g., W-2 or W-1) of the other waveguide.

In various instances, the neck 1928, 1938 can be fabricated similar tosome embodiments shown in FIG. 7 . For example, in some instances, thefirst inner vanishing core size (ICS-1), the first outer core size(OCS-1), and the spacing between the plurality of longitudinalwaveguides can be simultaneously and gradually reduced between the firstend and the second end along the optical element to an intermediatelocation (e.g., the neck coupling section), and simultaneously andgradually increased from said intermediate location to the second enduntil the second inner vanishing core size (ICS-2) and the second outercore size (OCS-2) are reached. Some embodiments may be flexible, whilesome embodiments may not be flexible.

To accomplish the function of an MCF-WDM device, one of the exampleembodiments of the combined SDM-WDM devices described above may befusion spliced to a fanout device. To fabricate a single device withreduced number of splices, one or more channel(s) (e.g., the pumpchannel(s)) may be introduced via an access region of the modified MCFadd-drop multiplexer as shown in FIG. 14 or FIG. 15 . Either one or bothof “direct access channels” may be used to introduce pump channels forco- and/or for counter-propagating pumping. In this case, the crosssection of the access region may be modified from the add-dropmultiplexer design as shown in FIG. 20 (e.g., side-polished region foraccessing the fiber). In this example, the cross-section 1950 shows aside-polished region 1951 configured to provide an accessing hole forthe fiber carrying light at W-2 (e.g., pump light at 980 nm), which isadjacent the fiber carrying light at W-1 (e.g., signal light at 1550nm). The cross section of the “middle portion” may also be modified fromthe add-drop multiplexer design and is shown in FIG. 19A after the fibercarrying light at W-2 is installed.

Various implementations described herein can be modified from theexamples shown. For example, the number of WDMs in the WDM-fanout deviceand/or the number of cores of the MCF can be different than those shownand described. For example, the number of WDMs in the WDM-fanouot deviceis not limited to the number of WDMs shown in the figures. As anotherexample, the number of cores of the MCF is not limited to the number ofcores shown in the figures. In addition, the number of WDMs in theWDM-fanout device and the number of cores of the MCF can be differentfrom each other. For example, the number of WDMs in the WDM-fanoutdevice does not necessarily have to equal the number of cores of the MCFto which the WDM-fanout device is coupled.

FIG. 19A shows 4 WDMs 1911A, 1911B, 1911C, 1911D in the WDM-fanoutdevice 1910 represented by 4 pairs of adjacent waveguides. Each pair ofadjacent waveguides includes a first waveguide for light at a firstwavelength (e.g., Wavelength-1 or W-1) and second waveguide for light ata second wavelength (e.g., Wavelength-2 or W-2). For example, W-1 can besignal light at 1550 nm and W-2 can be pump light at 980 nm. In otherexamples, W-1 can be pump light and W-2 can be signal light. Otherwavelengths are also possible.

As set forth herein, the light propagating in the adjacent first andsecond waveguides of the WDM-fanout device 1910 can be coupled into acore 1916, 1926, 1936, 1946, or 1956 of a MCF 1917, 1927, 1937, 1947, or1957 as shown in FIGS. 19B-19F. While the number of WDMs in theWDM-fanout device 1910 can equal the number of cores of the MCF (e.g., 4WDMs for a 4-core MCF), the number of WDMs in the WDM-fanout device 1910can be less than the number of cores of the MCF. FIG. 21A is a schematicdiagram of a cross-sectional view of such an example combined SDM-WDMdevice 1960. In FIG. 21A, the cross-sectional view of the exampleSDM-WDM device 1960 has a combination of 2 WDMs 1961A, 1961D (e.g., 2pairs of adjacent W-1/W-2 waveguides) and 2 single waveguides 1961B,1961C (e.g., 2 waveguides without adjacent waveguides) that can beconfigured to be coupled to a 4-core MCF.

A first WDM 1961A is represented by a pair of adjacent waveguides in theupper left of the cross-sectional view and a second WDM 1961D isrepresented by another pair of adjacent waveguides in the lower right ofthe cross-sectional view. Each of the other 2 waveguides 1961B, 1961C inthe upper right and lower left of the cross-sectional view can be asingle waveguide. For example, the single waveguide 1961B, 1961C can beconfigured to not couple light with another waveguide of the SDM-WDMdevice 1960.

Some such examples can be utilized for co-propagating andcounter-propagating light. For instance, the SDM-WDM device 1960 shownin FIG. 21A can be a WDM-fanout device D1 that can be configured to becoupled to a 4-core MCF 1, where diagonal cores of the MCF 1 cantransmit co-propagating light (e.g., two diagonal cores can transmitlight in the same direction as each other and the two other diagonalcores can transmit light in the same direction as each other) and theneighboring cores can transmit counter-propagating light (e.g., in twoneighboring cores, light can propagate in the opposite directions). TheMCF 1 can be a transmission MCF or an Erbium-doped fiber (EDF), namelyan Erbium-doped MCF. In some implementations, the device can be used inan amplifier. In some instances, the MCF 1 can be a submarine SDM linkwhich provides a communication link below a body of water such as a seaor ocean.

As shown within the dotted lines in FIG. 21B, the SDM-WDM device 1960shown in FIG. 21A (e.g., WDM-fanout device D1) can be coupled (e.g.,with splices 1965) with fanout device D2 having single waveguides (e.g.,without adjacent pairs of waveguides or WDMs). Device D2 can be anynon-WDM fanout device known in the art or yet to be developed. AlthoughFIG. 21B schematically illustrates device D1 and device D2 as triangularin shape, device D1 and/or device D2 can include a tapered region andoptical fibers extending from the tapered region (e.g., D1 and/or D2 caninclude portions of the fibers which are shown outside of the triangularshapes). Each of the two WDMs of device D1 can couple light at W-1 andlight at W-2 into a respective core of MCF 1. In FIGS. 21A-21B, W-1 canbe signal light at 1550 nm and W-2 can be pump light at 980 nm. In otherexamples, W-1 can be pump light and W-2 can be signal light. In otherexamples, other wavelengths are possible. FIG. 21B shows the pump lightentering an input waveguide of device D1. In some examples, D1 and D2may by combined in one device similarly to the device shown in FIG. 14and the pump light can enter combined device D1 via a direct accesschannel of device D1 such as described with respect to FIG. 20 .

Light at W-1 can be transmitted from MCF 2 (e.g., a transmission MCF)via device D2 and light at W-2 can be transmitted from a pump (e.g., a980 nm pump). Device D1 can combine the light at W-1 and W-2 and couplethe combined light into two respective diagonal cores of MCF 1 (e.g., a4-core Erbium-doped MCF) transmitting light from MCF 2 to MCF 1. Any ofthe coupling configurations shown in FIGS. 19B-19F can be used. Theother two diagonal waveguides of device D1 can transmit light receivedfrom MCF 1 (e.g., a transmission MCF) to MCF 2 (e.g., an Erbium-dopedMCF) via device D2.

In various examples, mode size adaptation and/or pattern adaptationfunctions may be utilized if the Erbium-doped fiber and transmissionfibers have different mode field diameters and/or core patterns. Spliceprotectors may or may not be used. All components within the dottedlines in FIG. 21B can be co-packaged as a single compact MCF-WDM device1970.

FIG. 22 is a schematic diagram of another example configuration 1980utilizing the device 1960 in FIG. 21A (e.g., WDM-fanout device D1)coupled with fanout device D2 without WDMs, e.g., as shown in the dottedlines. The configuration can mimic a single-core fiber amplifier pairused to amplify light in a counter-propagating pair of optical fibers.In various implementations, an amplifier 1980 can include two of theMCF-WDMs 1970 (e.g., shown in FIG. 21B) and a gain medium therebetweenMCF 1. For example, in FIG. 22 , device D1 and device D2 within thedotted lines can be similar to the configuration 1970 shown in FIG. 21B.For example, signal light from MCF 2 (e.g., a transmission 4-core MCF)can be transmitted via device D2 and coupled with pump light via deviceD1 into MCF 1 (e.g., an Erbium-doped MCF). This approach can provideco-propagating pumping (e.g., light at W-1 and light at W-2 propagate inthe same direction) for all four cores of the Erbium-doped 4C-MCF 1, 2from one end and 2 from the other end, as demonstrated in FIG. 22 . AnErbium-doped fiber amplifier (EDFA) is shown, but other implementationscan apply to other amplifiers, e.g., amplifiers using gain mediums otherthan Erbium-doped fiber.

As described with respect to FIG. 22 , various implementations caninclude a pair of the MCF-WDMs 1970 as described herein with a gainmedium MCF 1 therebetween. The gain medium can be an active MCF. Theactive MCF can have at least one pair of nearest-neighbor cores and atleast two pairs of next-nearest-neighbor cores. Thenext-nearest-neighbor cores can be configured to transmit light in asame direction and the nearest-neighbor cores can be configured totransmit light in the opposite direction. One of the two MCF-WDMs 1970can be configured to couple pump light into at least one pair of the twopairs of next-nearest-neighbor cores at one end of the active MCF 1, anda second of the two MCF-WDMs 1970 can be configured to couple pump lightinto another pair of the at least two next-nearest neighbor cores at theother end of the active MCF 1. Although the example amplifier 1980 shownutilizes a 4-core MCF 1, the number of cores is not limited to 4, e.g.,the number of cores can be less or more than 4. In addition, the arrayof cores can form a square pattern. In other implementations, non-squarecore patterns can also be used.

Any of the coupling configurations shown in FIGS. 19B-19F can be used.Additional devices (e.g., one or more gain flattening filters 1984and/or one or more isolators 1985) can also be used. Mode sizeadaptation can be integrated into devices D1 and/or D2, e.g., if MCF 1and MCF 2 are dissimilar. In addition, core pattern adaptation may alsobe achieved using devices D1 and D2 with different core patterns and/orspacing matching that of MCF 1 and MCF 2, respectively. Spliceprotectors may or may not be used. All components within the dottedlines in FIG. 22 can be co-packaged as a single compact MCF-WDM device1970. In the opposite direction, light from MCF 1 (e.g., Erbium-dopedMCF) can be transmitted to MCF 2 via devices D1 and D2.

FIG. 23 is a schematic diagram of another example configuration 1990utilizing the device 1960 shown in FIG. 21A. (e.g., WDM fanout deviceD1) coupled with fanout device D2 without WDMs. The configuration issimilar to FIG. 22 and includes a monitoring channel (e.g., a high lossloopback 1989). As shown, additional devices (e.g., one or more gainflattening filters 1984, one or more isolators 1985, one or morecouplers 1986, one or more line buildout (LBO) attenuators 1987, and/orone or more fiber Bragg gratings 1988) can also be used. Mode sizeadaptation and/or pattern adaptation may also be utilized. Spliceprotectors may or may not be used. All components within the dottedlines in FIG. 23 can be co-packaged as a single compact MCF-WDM device1970. Various implementations can be used with presently availablecomponents, but in a more compact and efficient form.

Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to preferredembodiments thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devices andmethods illustrated, and in their operation, may be made by thoseskilled in the art without departing from the spirit of the invention.For example, it is expressly intended that all combinations of thoseelements and/or method steps which perform substantially the samefunction in substantially the same way to achieve the same results arewithin the scope of the invention. It is the intention, therefore, to belimited only as indicated by the scope of the claims appended hereto.

What is claimed is:
 1. An optical coupler array for optical coupling ofa plurality of optical fibers carrying light at least at two wavelengthsW-1 and W-2 to an optical device, comprising: an elongated opticalelement having a first end operable to optically couple with saidplurality of optical fibers and a second end operable to opticallycouple with said optical device, and comprising: a common single couplerhousing structure; a coupling section; a plurality of longitudinalwaveguides, including at least one first waveguide and at least onesecond waveguide, each of said plurality of longitudinal waveguidesbeing positioned at a spacing from one another, each having a capacityfor at least one optical mode of a mode field profile, and acorresponding propagation constant, and each being embedded in saidcommon single housing structure, wherein at least one of said pluralityof longitudinal waveguides is a vanishing core waveguide, each saidvanishing core waveguide comprising: an inner vanishing core, having afirst refractive index (N-1), and having a first inner core size (ICS-1)at said first end, and a second inner core size (ICS-2) at said secondend; an outer core, longitudinally surrounding said inner core, having asecond refractive index (N-2), and having a first outer core size(OCS-1) at said first end, and a second outer core size (OCS-2) at saidsecond end, and an outer cladding, longitudinally surrounding said outercore, having a third refractive index (N-3), a first cladding size atsaid first end, and a second cladding size at said second end; andwherein said common single coupler housing structure comprises a mediumhaving a fourth refractive index (N-4) surrounding said plurallongitudinal waveguides, wherein a relative magnitude relationshipbetween said first, second, third and fourth refractive indices (N-1,N-2, N-3, and N-4, respectively), comprises the following magnituderelationship: (N-1>N-2>N-3), wherein a total volume of said medium ofsaid common single coupler housing structure is greater than a totalvolume of all said vanishing core waveguides inner cores and said outercores confined within said common single coupler housing structure, andwherein said first inner vanishing core size (ICS-1), said first outercore size (OCS-1), and said spacing between said plurality oflongitudinal waveguides, are simultaneously and gradually modified, inaccordance with a profile, between said first end and said second endalong said optical element, until said second inner vanishing core size(ICS-2) and said second outer core size (OCS-2) are reached, whereinsaid second inner vanishing core size (ICS-2) is selected to beinsufficient to guide light therethrough, and said second outer coresize (OCS-2) is selected to be sufficient to guide at least one opticalmode, such that: light traveling from said first end to said second endescapes from said inner vanishing core into said corresponding outercore proximally to said second end, light traveling from said second endto said first end moves from said outer core into said correspondinginner vanishing core proximally to said first end, and wherein, in saidcoupling section located proximal to said second end, at least one saidvanishing core waveguide is in coupling distance to another saidlongitudinal waveguide, said coupling distance and length of saidcoupling section are configured to couple light at least at wavelengthW-1 of at least one core mode of said at least one said vanishing corewaveguide with at least one core mode of another said longitudinalwaveguide while continuing the propagation of the light at saidwavelength W-2 in said another longitudinal waveguide.
 2. The opticalcoupler array of claim 1, wherein proximal to said second end, the lightat least at wavelength W-1 and the light at said wavelength W-2 coupleinto the same mode of said another longitudinal waveguide.
 3. Theoptical coupler array of claim 1, wherein said first inner vanishingcore size (ICS-1), said first outer core size (OCS-1), and said spacingbetween said plurality of longitudinal waveguides are simultaneously andgradually reduced between said first end and said second end along saidoptical element to said coupling section, and simultaneously andgradually increased from said coupling section to said second end untilsaid second inner vanishing core size (ICS-2) and said second outer coresize (OCS-2) are reached.
 4. The optical coupler array of claim 1,wherein said first inner vanishing core size (ICS-1), said first outercore size (OCS-1), and said spacing between said plurality oflongitudinal waveguides are simultaneously and gradually reduced betweensaid first end and said second end along said optical element, untilsaid second inner vanishing core size (ICS-2) and said second outer coresize (OCS-2) are reached.
 5. The optical coupler array of claim 1,wherein one of the wavelengths W-1 and W-2 is signal light and the otherof the wavelengths W-1 and W-2 is pump light.
 6. The optical couplerarray of claim 5, wherein the signal light is 1550 nm and the pump lightis 980 nm.
 7. The optical coupler array of claim 1, wherein one of thewavelengths W-1 and W-2 is signal light and the other of the wavelengthsW-1 and W-2 is another signal light.
 8. The optical coupler array ofclaim 7, wherein the signal light is 1550 nm and the another signallight is 1310 nm.
 9. The optical coupler array of claim 1, furthercomprising an access region configured to provide access to at least oneof said plurality of waveguides between said first and second ends. 10.The optical coupler array of claim 1, wherein said coupling section issubstantially straight.
 11. The optical coupler array of claim 1,wherein said coupling section has a neck.
 12. The optical coupler arrayof claim 1, wherein the plurality of longitudinal waveguides includes atleast one waveguide configured to not couple light with another of saidplurality of longitudinal waveguides in the optical coupler array.
 13. Amulticore fiber-wavelength division multiplexer (MCF-WDM), comprising: aWDM-fanout device comprising a first plurality of longitudinalwaveguides, said first plurality of longitudinal waveguides including atleast one waveguide configured to propagate light at a first wavelengthand at least one waveguide configured to propagate light at a secondwavelength, wherein the WDM-fanout device is configured to combine thelight at the first wavelength and the light at the second wavelengthinto a core of a multicore fiber; and a non-WDM fanout device opticallycoupled with the WDM-fanout device, the non-WDM fanout device comprisinga second plurality of longitudinal waveguides, wherein each waveguide ofthe second plurality of longitudinal waveguides is configured to notcouple light with another waveguide of said second plurality oflongitudinal waveguides in the non-WDM fanout device.
 14. The MCF-WDM ofclaim 13, wherein the first plurality of longitudinal waveguidesincludes at least one waveguide configured to not couple light withanother of said first plurality of longitudinal waveguides in theWDM-fanout device.
 15. The MCF-WDM of claim 13, further comprising oneor more isolators, gain flattening filters, couplers, attenuators,and/or fiber Bragg gratings.
 16. An amplifier, comprising two of saidMCF-WDMs of claim 13 and a gain medium therebeteween.
 17. The amplifierof claim 16, wherein said gain medium is an active MCF, said active MCFhas at least one pair of nearest-neighbor cores and at least two pairsof next-nearest-neighbor cores, wherein said next-nearest-neighbor corestransmit light in a same direction and said nearest-neighbor corestransmit light in the opposite direction, and wherein one of the two ofsaid MCF-WDMs couples pump light into at least one pair of the at leasttwo pairs of next-nearest-neighbor cores at one end of said active MCF,and a second of the two of said MCF-WDMs couples pump light into anotherpair of the at least two pairs of next-nearest-neighbor cores at theother end of said active MCF.
 18. The amplifier of claim 16, wherein thegain medium is an Erbium-doped fiber.
 19. The amplifier of claim 16,further comprising a monitoring channel.